Hodgkin Lymphoma and adoptive immunotherapy: An overview of current research

A recent article by Ho, et al. in Blood Advances¹ discusses adoptive immunotherapy for the treatment of classic Hodgkin lymphoma (cHL). Despite treatment options such as brentuximab vedotin and programmed cell death-1 (PD-1) checkpoint inhibitors, significant challenges remain in treating patients who are ineligible for transplant, or those who progress after transplant. Ho and colleagues’ discussion of relevant clinical trials, current challenges, and possible future strategies to improve treatment options for cHL are summarized in this article.

Chimeric antigen receptor (CAR) T-cell therapy, a type of adoptive immunotherapy, involves the genetic engineering of T cells to express CARs, and these receptors redirecting T cells toward tumor antigens. Autologous T cells are harvested from patients, engineered, and expanded ex vivo, then re-infused back into the patient to target and kill cancer cells. CAR T-cell therapy has been used to successfully treat B-cell malignancies, specifically non-Hodgkin lymphomas and relapsed or refractory (R/R) acute lymphoblastic leukemia. The role of CAR T-cell therapy in patients with R/R cHL however remains uncertain.

The immunosuppressive tumor microenvironment in cHL 

cHL is a lymphoid neoplasm characterized by the presence of Hodgkin Reed-Sternberg (HRS) cells admixed with a much larger population of non-malignant inflammatory cells.² To consider novel adoptive T-cell treatment strategies, an understanding of the immune evasion in cHL and its immunosuppressive tumor microenvironment (TME) is important. HRS cells are characterized by cell surface markers CD15 and CD30 and loss of typical B-cell surface markers such as CD19. Although they account for only 1–2% of tumor cell mass, they thrive in a lymphocyte rich TME. Mechanisms of HRS immune evasion in cHL include:

• Downregulation and alteration of HLA class I and II molecules causing interruption of tumor-antigen presentation.^3-5
• Secretion of various chemokines (CCL5, CCL17, and CCL22) and cytokines (IL-7) to recruit regulatory T cells, which in turn secrete IL-10 and TGF-β which inhibit cytotoxic T-lymphocyte (CTL) activity.^6,7
• Expression of Fas ligand which can induce apoptosis of CTLs.^6,7
• Recruitment of tumor-associated macrophages which support the immunosuppressive TME.
• Frequent expression of checkpoint ligands—through various mechanisms including Epstein Barr virus (EBV) infection—such as programmed death receptor ligand-1 (PD-L1) and PD-L2 which inhibit T cell activation and proliferation.^5,8,9

EBV-targeted T cells

Infection with EBV is often involved in the pathogenesis of cHL: approximately 40% of patients with cHL have EBV-positive disease.¹⁰ EBV-specific T cells have been used with significant clinical success to treat EBV-associated post-transplant lymphoproliferative disease. However, the expression of EBV antigens on HRS cells in EBV positive cHL follows the type II latency pattern, in which only weakly immunogenic EBV antigens are expressed. These include latent membrane protein (LMP)1, LMP2, EBV nuclear antigen 1 and BamH1-A right frame 1. EBV-positive HRS cells also secrete IL-10, which further inhibits cytotoxic T-cell response to viral antigens. This is in contrast to post-transplant lymphoproliferative disease in which the entire repertoire of EBV antigens is expressed (type III latency pattern).

After an early study of autologous CTLs directed against a nonspecific array of EBV antigens demonstrated limited clinical responses in cHL,¹¹ LMP-specific CTLs were developed to improve specificity for antigens seen in the type II latency pattern of cHL. Study findings are summarized in Table 1. Patients did not undergo lymphodepletion prior to infusions.

Table 1. Results of EBV-targeted T cells in clinical trials*

In the study by Bollard, et al.,¹² 50 patients with EBV+ lymphoma received infusions of LMP-specific T cells. Of these, 25 had cHL, eight with active disease. The overall response rate (ORR) for patients with active cHL was 50%. Interestingly, although cHL is associated with the type II latency pattern of EBV antigen expression, a small number of patients were found to have type III latency pattern secondary to comorbid immunosuppression. In the eight patients with active disease, three had type III latency and five had type II. All three patients with type III latency achieved complete response (CR) whereas the ORR for type II latency pattern was just 10%. This suggests differences in tumor immune evasion may exist, that are more easily overcome in patients that are immunosuppressed.

To further the efficacy of EBV-directed therapy, Bollard, et al.¹³ targeted the immunosuppressive TME by transducing EBV-specific CTLs with a dominant-negative TGF-β type 2 receptor (DNRII). Through forcing DNRII expression, T cells were resistant to TGF-β in vitro, retaining their tumor antigen-specific activity. Although only small a phase I trial of patients with extensively pre-treated R/R EBV-positive cHL, four of seven patients with active disease achieved a response to treatment (two achieved CR, one achieved PR and four had stable disease [SD]). Two patients who had previously received LMP-specific CTLs without DNRII¹⁴ showed a greater response to infusion with DNRII CTLs. In both studies, infusions were found to be safe.

Infusion of donor-derived allogenic EBV-specific CTLs has been shown to be safe and produce clinical responses in some small clinical trials.^15,16 The use of partially matched banked EBV-specific CTLs (targeting LMP, BARF-1 and EBNA-1) is currently being explored (NCT02287311) and may be beneficial for those with rapidly progressive disease requiring urgent treatment.

CD30 CAR T cells

CD30, a member of the tumor necrosis factor receptor family, has anti-apoptotic and pro-survival effects on cells. It is expressed highly on HRS cells and only minimally on non-malignant activated B and T cells, thus limiting the possibility of on-target off-tumor toxicity. The success of brentuximab vedotin, a CD30 monoclonal antibody-drug conjugate, suggests it is an ideal therapeutic target.

Three published trials have considered CD30-targeting CAR-T cells and are summarized in Table 2. Of note, all three studies found that treatment was well tolerated. Furthermore, despite previous concern that CD30 CAR-T cells could impair cell-mediated immunity given that a small fraction of activated B and T cells express CD30, no significant increase in infections was seen in any of the trials.

Table 2. Results of CD30-targeted T cells in clinical trials*

Multiple clinical trials of CD30-targeted CAR-T cells are ongoing. One such study (NCT03602157) is investigating CD30 CAR-T cells that have been engineered to co-express CCR4. CCR4 is the ligand for chemokines CCL17 and CCL22, which are secreted by HRS cells and aid immune evasion and inhibition of immune response. These CD30 CAR-T cells with CCR4 have been shown to improve tumor-trafficking and anti-tumor activity in a mouse model of cHL.²⁰ Furthermore, anti-CCR4 monoclonal antibodies were effective in depleting CCR4⁺ T cells and preventing migration of regulatory T cells in vitro and thus may present a further novel combination treatment strategy. Finally, several studies (NCT04288726, NCT01192464) are investigating EBV-specific CTLs that have been engineered to express anti-CD30 CAR.

Targeting the tumor microenvironment

Although CD19 is not expressed on HRS cells, CD19 targeted CAR-T cells have been considered in R/R cHL as a means of targeting non-malignant B cells in the TME, as well as CD19⁺ B cells in circulation that may represent HRS precursors. In a pilot study of four patients with R/R cHL and no curative therapy options, therapy was well tolerated; however, observed responses were transient: one had CR, one had PR, one had SD and one had PD at 1 month follow up.

CD123 is present on approximately 60% of cHL cell populations (as alpha chain of IL-3 receptor) as well as other cells in the TME such as M2-type tumor-associated macrophages (which suppress immune response and promote tumor infiltration). A pre-clinical study of anti-CD123 CAR-T cells demonstrated their ability to eradicate cHL cells, develop immunological memory and resist suppression by M2-macrophages.²¹

The potential to combine infusion of CD30 CAR-T cells with CD19 or CD123 CAR-T cells may offer further treatment strategies and is currently being explored (NCT03125577).

Conclusion

The development of adoptive immunity for the treatment of cHL has not accelerated as quickly as with other B cell malignancies; however, EBV-specific CTLs and CD30 CAR-T cells have shown promising responses in early clinical trials in patients with R/R cHL. Understanding the unique immunosuppressant tumor microenvironment in cHL and its mechanisms of immune evasion may offer opportunity to further improve treatment strategies, such as the addition of CD19 or CD123 CAR-T cells. Building on the success of adoptive immunotherapy in EBV+ patients, trials examining specific tumor-associated antigens—regardless of EBV status—are also now underway.

Furthermore, treatment strategies that combine CAR-T cells with checkpoint inhibitors, CAR-T cells that have been engineered to secrete anti-PD-1 checkpoint inhibitors, or T cells that have been genetically altered to disrupt PD-1 expression (via CRISPR-Cas9 gene editing) may enhance anti-tumor action and improve persistence of transferred T cells.