Activity Transcript

Corey S. Cutler, MD, MPH, FRCPC: Good evening, everyone, and welcome to this Medscape Oncology event titled, 2021 Winter Updates in EBV-Positive Posttransplant Lymphoproliferative Diseases. My name is Corey Cutler. I'm the Medical Director of the Stem Cell Transplant Program at the Dana-Farber Cancer Institute in Boston. It's my pleasure this evening to have with me two very distinguished faculty in the field. First, Dr Susan Prockop, who is the Associate Director of Clinical and Translational Research here in the Stem Cell Transplant Program at the Dana-Farber pediatric site, as well as Dr Pierluigi Porcu, who is the professor of medical oncology and the Director of the Division of Hematologic Malignancies and Stem Cell Transplantation at the Sidney Kimmel Cancer Center of Thomas Jefferson University in Philadelphia.

Tonight, we're going to discuss EBV-positive posttransplant lymphoproliferative disease. I will begin the program by discussing some overview slides, including incidence, timing, risk factors, and some general outcomes of PTLD.

So by way of introduction, we know that PTLD is rare. It does not happen very often in our careers, even as transplanters. We know that PTLD is driven largely by EBV, and it is an EBV infection of B cells. The vast majority of transplant-related PTLD or stem cell transplant-related PTLD are in fact related to EBV-positive B cells. And the majority or about half of solid organ transplant PTLDs are related to EBV infection of B cells.

Because this is such a rare occurrence, there are really no approved therapeutics. However, the standard of care in our field is to provide B-cell depletion and a reduction in immunosuppression to allow the immune system to take care of the problem. However, once we get to rituximab-refractory disease, things really become much more difficult. There is no standard of care here. We are in the realm of research, and survival is very poor.

In terms of terminology, there are several different subtypes of PTLD. Nondestructive PTLD we are not going to discuss this evening; we are really going to focus on monomorphic PTLD, which is generally an aggressive lymphoma, a large-cell lymphoma type of presentation. Very rarely there is a T-cell variant of this, and even rarer is a Hodgkin lymphoma type PTLD.

We know that in stem cell transplantation, a very small minority of our patients will develop this complication -- about 3% of our subjects. And this incidence varies depending on donor type and degree of immunosuppression that is required to be used in the setting of that different donor type. It tends to occur relatively early after transplantation, just a few months, but later cases, of course, can occur.

When we talk about solid organ transplantation, the incidence is about the same -- about 2% -- and here that incidence is driven largely by the organs that are transplanted the most frequently. So it is relatively uncommon after kidney transplantation, but it becomes very prevalent when one gets into transplantation of larger organs that require much heavier immune suppression at the time of the transplant procedure.

Differentiating hematopoietic transplant from solid organ transplant is the occurrence of a second wave of PTLD after solid organ transplant. This occurs 7 to 10 years following the solid organ transplantation and actually tends to be less related to EBV at that time.

As I mentioned before, the major risk factors for development of PTLD are the degree of HLA mismatch and thus the degree of immunosuppression that is required after transplantation. Of course, age is related, and then transplant types that involve less or fewer T cells. So umbilical cord transplant and T-cell depletion strategies tend to be more commonly associated with EBV PTLD.

Once EBV PTLD does occur, outcomes when they are adverse are almost always related to that occurrence of PTLD itself. In transplantation, we would ascribe almost all deaths after PTLD to the PTLD. And as you can see here between 50 and 65 percent of all deaths after PTLD, both in the stem cell transplant and in the solid organ transplant setting, are in fact related to PTLD.

As I mentioned, outcomes in the frontline are reasonable with rituximab and reduction of immunosuppression, but once one gets into second-line therapy or rituximab-refractory cases, you can see that outcomes really are quite poor, more so in stem cell transplantation than they are in solid organ transplantation.

So there are some standard therapeutics for this. This very nice schematic discusses the main things we can do. As I mentioned, anti-CD20 monoclonal antibodies are the mainstay of therapy and reduction of immune suppression to allow T-cell immunology and T-cell immunity to work on the infected T cell. And we're going to get into some of the more experimental approaches with our speakers in a minute, discussing novel agents and novel cellular therapies. This is really represented here on this slide. The main issue when we get into preemptive therapies and frontline therapies for PTLD is that with a reduction of immune suppression, one gets into the significantly elevated risks of solid organ graft rejection as well as acute graft versus host disease after stem cell transplantation.

Here are some slides on the role of rituximab. We all understand rituximab targets B cells, which are the cells that are affected in PTLD and are the cells that are transformed. There are novel or second- and third-generation monoclonal anti-CD20 antibodies that are currently approved outside of PTLD that are being tested in the PTLD setting. And then there are a number of additional agents that are being tested in PTLD. Some of the agents are shown here, and you're going to hear about some of these agents very shortly from our speakers.

With that, I'm going to move and ask Dr. Prockop to take over, and she is going to discuss the management of rituximab-refractory EBV PTLD.

Susan Prockop, MD: Thank you so much, Dr. Cutler, and the audience for logging in to this event. I'm going to be talking about the use of EBV-specific cytotoxic T cells, highlighting 2 interim analyses of ongoing trials that were presented at the recent ASH meeting.

So EBV-specific T cells as adoptive therapy for EBV-driven PTLD emerging after hematopoietic and solid organ transplant, actually has been around since the mid-1990s, and in the earliest studies as depicted on the left, EBV-specific T cells were generated using a method pioneered by Cliona Rooney and the group now at Baylor. So B cells are separated from a leukapheresis from a normal, healthy, EBV-seropositive donor, and those B cells are transformed with a laboratory strain of the Epstein-Barr virus. These transformed B cells present EBV antigen and surface professional antigen-presenting cells in co-culture with T cells from the same leukapheresis. This co-culture is restimulated weekly for about a month, over which period of time the EBV-specific T cells, as depicted in gold in this figure, are sensitized and expanded, and potentially alloreactive T cells, depicted in red, are not. This process takes about 8 to 12 weeks and was one of the real limitations in using this therapy effectively for patients at the time that they developed EBV PTLD.

In the 20 plus years since that time, there have been a number of different approaches to generating EBV-specific T cells and biospecific T cells in general. And the most commonly used for EBV, certainly, is depicted on the right. So this is a process that avoids the use for cultured professional antigen-presenting cells. So PBMCs are isolated from a donor and are cultured with a mix of immunogenic peptides for the viruses of interest as well as cytokines. And over a period of 10 to 14 days, you get expansion of the viral-specific T cells. In both of these instances, the T cells are then characterized and can be frozen for future use.

As I mentioned, there were challenges with generating these T cells from hematopoietic transplant donors for the recipients, or from solid organ transplant recipients prior to their transplant. And some of those limitations related to the timing. As I mentioned, it takes 8 to 12 weeks to generate a T-cell line using the initial method that’s appropriately cytotoxic. Another was donor availability. So it's difficult using these methods to generate effective T cells from seronegative donors. But the other limitations revolve around efficacy. So one is that we know that some viral-specific cytotoxic T cells generated in vitro, while showing effective cytotoxicity in vitro, fail to mediate responses in vivo. And the other is that in the HLA-disparate setting, if the infected cells are of recipient rather than donor origin, donor T cells may be restricted by a non-shared HLA allele and ineffective.

And so one of the advances in this field has been to really rely on third-party or banks of viral-specific T cells. And these overcome many of those limitations I just mentioned. So one is the timing becomes irrelevant, or the time it takes to generate the T-cell line becomes irrelevant, because they're ready for immediate off-the-shelf use. You can specifically generate these lines from donors where you know that the donor is seropositive for the virus of interest. You can avoid using T-cell lines that are restricted by HLA alleles where you predict they won't work. And in fact, in patients who fail to respond to an initial cycle of T cells, you can switch to a second line that's restricted by a different HLA allele and recognizes a different viral epitope. So the idea of switch therapy that improves the potential for responses. And then finally you can really ensure that your viral specificity is being mediated through a shared HLA allele.

And the development of these different therapies has really been an iterative process. So as well as the development of third-party T cells, groups have continued to develop, to improve the efficacy and the specificity of some of these donor-derived products, including making multi-viral-specific products.

There were two studies of tabelecleucel presented at the recent ASH meeting. The first was a retrospective combined analysis of data from single-center studies at Memorial Sloan Kettering, with a multicenter expanded access study of the tabelecleucel product. So this study looked at the potential clinical benefit in people with relapsed and refractory EBV PTLD, demonstrating an overall response rate of 62% in the hematopoietic transplant setting and 65% in the solid organ transplant setting, and then looked at overall survival by best overall response.

And here, I think there are two important messages. One being that those patients whose disease responded to adoptive T-cell therapy had improved overall survival compared to those who did not. So the patients who had a complete response had a 2-year overall survival of 86.2%, and the partial response is 86.5%, while those with stable disease and progression of disease had far inferior 2-year overall survival. But the other important point here is that those patients who had a complete response had similar overall survival to those with a partial response. This is obviously different than what we would expect in the setting of chemotherapy-based approaches, and one of the things that have pretty consistently been seen across all the different studies of viral specific T cells.

The second study that was presented at ASH involving tabelecleucel was a planned interim analysis of a phase 3 trial of tabelecleucel in patients who had EBV PTLD refractory to rituximab after hematopoietic transplant, and two cohorts of patients after solid organ transplant, one with disease refractory to ritux, and one with disease refractory to rituximab combined with chemotherapy. All of these patients received 3 weekly infusions of 2 million T cells per kg and had a disease assessment performed at day 35. They were eligible to receive subsequent cycles of T cells either from the same or a different donor. They were followed, at this interim analysis, the patients assessed were followed for at least 6 months, but on study patients are assessed for durability of response through 2 years and survival through 5 years.

There were 38 patients available for interim analysis, 14 after hematopoietic and 24 after solid organ transplant. And I think it's notable that 11 of these patients have ECOG scores of 2 or greater, sort of reflecting the severe disease that's seen in this patient population. And a significant portion of these patients had prior chemotherapy. In addition, 33 of 36 patients evaluable had PTLD-adapted prognostic index that was intermediate or high risk.

So patients received a median of two and a half cycles of tabelecleucel. And you can see here, as expected based on the epidemiology of PTLD in the solid organ compared to hematopoietic transplant setting, that the time to diagnosis from transplant was longer in the solid organ transplant cohort. And the time from diagnosis of PTLD to treatment with adoptive T cells was longer in the solid organ transplant setting, reflecting the time that these patients received alternative therapies and chemotherapy.

The objective response rate in both cohorts was 50%, with the best overall response, a complete response, in 26.3% of patients, and partial response in 23.7% of patients, with a median time to respond in all patients of 4.1 months. And as had been seen in the previous studies, those patients who respond have a higher, in this analysis, 1-year overall survival. So responding patients have a 1-year overall survival of 89.2%, compared to those who don’t respond to therapy of just 32.4%.

In terms of tolerability, 23 of these patients had grade 3 or greater treatment-emergent adverse events, and 5 of these patients had fatal events, but none of the fatal events were treatment related, and none of the events were GvHD related to adoptive T cells or organ rejection related to the adoptive T-cell therapy. And there was no recurrent treatment-related adverse events except for pyrexias.

So in conclusion, they've demonstrated that in this interim analysis, an overall response rate of 50% with a median time to respond of 1.1 months, and it continues to show the tolerability of this adoptive cell therapy for patients without alternative therapies.

The second interim analysis that was presented at the recent ASH meeting was posoleucel, which is a multi-viral specific product, and in this instance, the product is being used in a prophylactic regimen. The goal of this study is to decrease the incidence of severe viral infections in patients posttransplant with a background that approximately 70% of high-risk patients will experience clinically significant viral infections.

So these high-risk patients -- by virtue of having mismatched transplants or cord blood transplants or based on their absolute lymphocyte count and CD4 count at the time of enrollment -- started therapy 15 to 49 days after hematopoietic transplant and received 4 x 10⁷ T cells per dose, with doses given once every 14 days, up to 7 doses. And the primary endpoint for this study was the number of clinically significant viral infections through week 14, and the secondary endpoint, the number of clinically significant viral infections through week 26.

Twenty-three patients were evaluable for this interim analysis and demonstrated that 3 had clinically significant infections at the week 14 mark. Two had reactivation of CMV requiring initiation of valganciclovir, and one had EBV requiring initiation of rituximab. Two additional patients who were followed through the 26-week time point had reactivation, 1 of CMV and 1 of the flu virus. There was no end-organ or invasive disease by either time point.

The safety and tolerability is presented here, with no unexpected treatment-emergent adverse events. Six of the 23 patients developed grade 2 to 4 acute graft versus host disease. And there was no association between GvHD and the number of HLA alleles matched with the recipient in the third-party T cells, and no association with the number of doses of T cells administered.

So in this ongoing open-label cohort of a phase 2 multi-viral prevention trial, the data was sufficient that the trial is being expanded into a phase 3, blinded, placebo-controlled trial, again looking at prevention of severe infection with 6 targeted viruses.

And really, I think one of the most important aspects of these therapies is that they're finally starting to move beyond the boutique centers that have been administering these therapies now for almost 2 decades to really more broadly accessible therapy. Highlighted here are a few of the additional multicenter trials looking at adoptive T cells for EBV PTLD that are available for a broadening number of patients. And I think that's really the most important aspect of this therapy. And I think I'm going to turn it over now to Dr. Porcu to talk about other alternative treatments for EBV-positive lymphoma.

Pierluigi Porcu, MD: Thank you everyone, a pleasure to be on this program. And over the next few minutes, I'm going to describe a different strategy and approach to EBV-positive lymphomas, including PTLD.

So, as we know now, a number of lymphomas can be associated with EBV. I think we've known for a while, of course, that immunodeficiency-associated lymphomas such as PTLD or HIV-positive lymphomas are very often associated with EBV. We also have known that certain rare subtypes of T-cell and NK-cell lymphomas are universally associated with EBV, such as extranodal NK/T-cell lymphoma, for example. But I think it now is becoming more clear that a variety of also common histology lymphomas in immunocompetent patients can be associated with EBV, such as diffuse large B-cell lymphoma, various types of peripheral T-cell lymphoma, and Hodgkin lymphomas, of course, as well.

So, over time, there has been an interest in developing strategies to use the virus in these lymphomas potentially as a targeted therapy with the idea of using essentially the proteins that are expressed by the virus as a platform for targeting personalized drug therapy.

One of the very first examples of this was published more than 10 years ago in Blood by Dr Faller’s group at Boston University and colleagues. And the idea was a combination of an HDAC inhibitor with an antiviral drug. The mechanistic rationale for the use of this combination is shown on the right. What's important is that even in this very initial pilot study, in which the HDAC inhibitor was arginine butyrate while the antiviral was ganciclovir, there was a very significant and encouraging efficacy in a variety of different diseases, including NK lymphoma, diffuse large B-cell lymphoma, and PTLD.

The challenge with this approach was the fact that arginine butyrate is a relatively inefficient HDAC inhibitor, and it also requires a continuous intravenous infusion, so it was really not doable logistically. And this led to the next study I'm going to present.

However, just to review right here on the right panel, the mechanism for this combination. This is based on the fact that HDAC inhibitors in the cell that are infected by EBV induce the expression of a certain set of EBV genes that are called lytic genes. Now one of these genes is called the BZLF1. It's the master transcription regulator for the lytic cycle of EBV. And once this BZLF1 is expressed, there's a cascade of additional gene expression that includes a variety of kinases included by the virus. One of them is called BGLF4. We know that BGLF4 activates ganciclovir by doing a monophosphorylation. And once a monophosphorylated ganciclovir is in the cells, cellular kinases are triphosphorylated, and then this actually gets included in the DNA, inhibiting the cellular DNA polymerase and causing cell death. So in this case the ganciclovir is used as a cytotoxic drug, not necessarily as an antiviral drug, and the use of the virus is just related to the fact that the virus is necessary for the activation of the drug.

Just to go into this mechanism a little bit more in detail, this shows that a number of nucleoside analogues, as you know, nucleoside analogues have been probably one of the most successful class of drugs ever produced. They're used as antivirals, and very often they're used as anti-cancer drugs. A good example would be fludarabine and endostatin. Well, ganciclovir and acyclovir, to be activated, they use a viral kinase which I just showed before called BGLF4. Another nucleoside analogue, AZT, is activated by a different type of kinase also by EBV, called BXLF1. Regardless of which kinase activates which nucleoside analogue, these nucleoside analogues are monophosphorylated, and then the kinase is making it into a triphosphorylated nucleoside analogue.

This is where it becomes important to distinguish the nucleoside analogue in terms of their ultimate effect. Because if the effect is, for example, inhibiting viral replication, then what you want is a triphosphorylated nucleoside analogue that is very efficient in inhibiting the viral DNA polymerase, and it does not inhibit very much the cellular DNA polymerase. So acyclovir, for example. Acyclovir inhibits well the EBV DNA polymerase. It is not very efficient in inhibiting cellular DNA polymerase, and therefore causes inhibition of replication of the virus without necessary toxicity. On the other hand, ganciclovir is very efficient in inhibiting both the viral DNA polymerase and the cellular DNA polymerase and therefore causes growth inhibition, which is clinically evident because as everyone knows, ganciclovir can cause significant myelosuppression in patients. So this was the rationale for selecting ganciclovir in this study and also in the previous study.

So the final results of this study were presented at ASH just last year using nanatinostat, which is a class 1 very potent orally bioavailable HDAC inhibitor, in combination with valganciclovir. So the study was designed as an open-label phase 1b/2. It was open in the US and in Brazil as well. There was an initial dose range in phase 1b with 25 patients, and then eventually a phase 2 expansion under RP2D, which was defined as nanatinostat orally given 200 milligrams daily, 4 days per week, and valganciclovir 900 milligram daily.

The eligibility for this clinical trial included any type of EBV-associated lymphoma defined by local pathology by EBER expression. At least 1 prior therapy with no curative option for investigator. Fairly standard, in fact, fairly liberal organ function and hematological values. Performance status equal to 0 to 2, no CNS disease. Patients with HIV-positive lymphoma were eligible in the phase 1, but they were not eligible for the phase 2 based on a lack of a signal of efficacy, at least based in the phase 1. Patients were evaluated in terms of response assessment by PET/CT scan, with Lugano classification.

This shows the patient demographics on the study altogether, all the 55 patients. Median age 60. This was the male to female ratio. Most of the patients had good performance status; there were just a few patients with ECOG 2. The median number of prior therapies was 2, but the range of therapies for all the groups was fairly large, with some patient up to 11 prior therapies.

This shows the therapies that were received by these patients, which also included, in fact, EBV-cytotoxic T lymphocytes in 5 patients. Most of the patients were refractory to the last therapy or had exhausted all therapy per investigator.

This shows the breakdown of the histologies. Fairly broad representation of different histological types, with DLBCL, NK lymphoma, peripheral T-cell lymphomas, and a variety of immunodeficiency-associated LPDs, including 4 patients with PTLD.

When it comes to safety, there was no unexpected toxicity. The primary toxicities were hematological, as expected with both drugs -- thrombocytopenia and neutropenia, some acute kidney injury initially. As we were sort of developing the recommended phase 2 dose and adjusting the dose-escalation part, once we got to the phase 2 study, all these toxicities were significantly mitigated. Certainly there were no drug-related deaths occurring in the treatment, and in the phase 2, a very small number of grade 3/grade 4 toxicities.

Looking at the responses, looking for singular responses, it was encouraging to see that responses were observed in most subtypes, including complete responses. For example, in a patient with DLBCL. Two patients with complete response here. Extranodal NK lymphoma, peripheral T-cell lymphomas, and immunodeficiency-associated LPDs. The complete responses were particularly encouraging because, particularly DLBCL and peripheral T-cell lymphomas, these are lymphomas that are highly resistant to therapy, and therefore it was really encouraging to see these responses in these patients.

The median duration of response was 10.4 months as shown in this slide on the left. We did an initial preliminary analysis of the association between EBER positivity and response. EBER was done in a local institution, but this is based on a centralized assessment of EBER positivity. And according to this analysis, there was no clear signal of association between the level of positivity of EBV and response.

The swimmer's plot here shows the duration of the responses for the patients, which is telling. As you can see, there are some patients who have ongoing prolonged responses all the way up to 28 months here, a patient with DLBCL. The same for some of the T-cell lymphomas. Responses in immunodeficiency-associated LPDs, the number is smaller, a little less perhaps encouraging, although there was a complete response in a patient with PTLD. In particular here, this is sort of driven by the fact that the patients with HIV-associated lymphomas did not have responses. We've seen responses in patient with Hodgkin lymphoma as well.

So the conclusion of this study is that this oral therapy -- nanatinostat and valganciclovir -- is really kind of an EBV-targeting therapy with a clear antitumor rationale in these lymphomas. The final results presented at ASH show that it is well tolerated, with reversible low-grade toxicity. Lymphoma subtypes of different lineage respond to the nanatinostat and valganciclovir, irrespective of the patient immune status because we saw responses both in immunocompetent and immunocompromised patients, and also irrespective at least based on the dataset, on degree of EBER positivity. The complete responses were observed in different subtypes. Median duration of response is encouraging. Plasma EBV levels were detected at baseline in 72% of the patients, but we observed -- these are very preliminary data at this point -- but higher level of baseline and during therapy appear to be more often found in nonresponders. So we are pursuing that to see whether this potentially could be a predictor response.

So overall, this is a safe, active oral therapy for patients with EBV-positive lymphoma, feasible also in resource-limited, infrastructure-poor communities, because based on oral therapy, I think the logistical requirements for the use of this combination are certainly favorable. There is a multicenter global phase 2 basket study called NAVAL-1 that's currently enrolling patients with relapsed/refractory lymphoma, and this is NCT05011058.

Finally, just one slide on 2 or 3 clinical trials that are ongoing at this time. These trials are not specific for PTLD or for EBV-positive lymphomas, but they allow enrollment of patients with PTLD. So I think that should definitely be considered for patients who have refractory disease. There is a logical rationale to use some of these drugs. Everolimus clearly has shown a mechanism of interest in EBV-positive lymphomas. HDAC inhibitors, as I showed, clearly there is kind of an interest, and the combination of everolimus and lenalidomide based on the combined effect on EBV and immune response. With this, thank you for your participation. I give this back to Dr. Cutler. Thank you.

Dr Cutler: That was fantastic. Thank you, Dr. Porcu and Dr. Prockop, for really very nice presentations on really innovative approaches to the management of this disease.

Dr Prockop: Thank you for the invitation to do this. It was really educational for me.

Dr Porcu: Same here. Thank you. It was great to participate. I think PTLD is a very important and growing topic relevant to our patients. So it was great to have this program. Thank you.

Dr Cutler: Great. And again, to thank Medscape Oncology for putting this program together for all of us, and with that, we will wrap up the program. Thank you, everyone, for attending this evening.

This transcript has been edited for style and clarity.