Why do B cell lymphoma fail to elicit clinically sufficient T cell immune responses?

Current advances, problems and prospects for vaccine-based immunotherapy in follicular non-Hodgkin's lymphoma

Despite advances in chemotherapy, radiotherapy and combined modality treatment, a significant proportion of non-Hodgkin's lymphomas remain incurable. The disease usually responds well to chemotherapy or radiation, but relapses are observed within months to a few years, with frequent failure of subsequent therapies. High-dose chemotherapy with or without radiation and autologous or allogeneic hematopoietic stem cell transplantation provide higher cure rates and longer remissions in certain patients with aggressive lymphomas. However, the higher treatment-related morbidity and mortality of high-dose chemotherapy has driven a search for new and more tumor-specific treatment modalities, such as immunotherapy. Tumor antigens expressed by B-cell lymphomas, such as the "idiotype antigen", are seen as unique and specific target molecules for direct lymphoma immunotherapy. This review will delineate advances, problems and prospects for approaches to anti-B cell lymphoma immunotherapy where pre-clinical studies and proof of principle have been directly translated to patient care.

Use of adenoviruses encoding CD40L or IL-2 against B cell lymphoma

Some B cell lymphomas lack important costimulatory properties that could prevent them from being used as cell based vaccines. Infection of A20 B lymphoma cells with a replication-defective adenovirus encoding murine (m) CD40L, but not mIL-2, produces an antigen presentation phenotype with upregulation of MHC Class I/II, induction of B7-1/2 molecules and production of MIL-12 and MIP-1alpha. Subcutaneous vaccination with irradiated Ad-mCD40L-infected- or Ad-mIL-2-infected-A20 cells generated A20-specific CD8+ T cell responses and cross reactive A20 Ig antibodies. Only vaccination with Ad-mCD40L-infected A20 cells produced a significant delay in tumor growth and long-term survival (p = 0.0039). Stronger protective immunity to A20 challenge was generated by intravenous priming with A20 cells infected with Ad-mCD40L, Ad-mIL-2 or their combination followed by a boost immunization with A20 cells activated with syngeneic fibroblasts expressing CD40L. Compared to Ad-LacZ-infected A20 priming, the combination priming was most effective followed by Ad-mCD40L and Ad-mIL-2 (p = 0.0027, p = 0.0027, p = 0.0163 respectively). Significant A20-specific CD8+ T cell-mediated cytotoxicity was only demonstrated in splenocytes from these groups of vaccinated animals. By contrast, ELISPOT assay of splenocytes from all A20 prime/boosted vaccinated groups demonstrated increases in gamma-interferon release by T cells elicited by in vitro stimulation either with A20 cells or another syngeneic 2PK-3 lymphoma, indicating the presence of cross reactive immunity. Similarly anti-A20 immunoglobulin antibodies generated after vaccination were not necessarily A20 idiotype-specific. Direct therapy of pre-established tumors was achieved with the combination of Ad-mCD40L and Ad-mIL-2 given at Days 4 and 8 at the tumor site with a significant long-term survival of 85% of tumor-bearing mice (p = 0.0001). Our study strongly supports the use of Ad-CD40L and Ad-IL-2 combination therapy for the treatment of patients with B cell lymphoma.

Vaccine and antibody-directed T cell tumour immunotherapy

Clearer evidence for immune surveillance in malignancy and the identification of many new tumour-associated antigens (TAAs) have driven novel vaccine and antibody-targeted responses for therapy in cancer. The exploitation of active immunisation may be particularly favourable for TAA where tolerance is incomplete but passive immunisation may offer an additional strategy where the immune repertoire is affected by either tolerance or immune suppression. This review will consider how to utilise both active and passive types of therapy delivered by T cells in the context of the failure of tumour-specific immunity by presenting cancer patients. This article will outline the progress, problems and prospects of several different vaccine and antibody-targeted approaches for immunotherapy of cancer where proof of principle pre-clinical studies have been or will soon be translated into the clinic. Two examples of vaccination-based therapies where both T cell- and antibody-mediated anti-tumour responses are likely to be relevant and two examples of oncofoetal antigen-specific antibody-directed T cell therapies are described in the following sections: (1) therapeutic vaccination against human papillomavirus (HPV) antigens in cervical neoplasia; (2) B cell lymphoma vaccines including against immunoglobulin idiotype; (3) oncofoetal antigens as tumour targets for redirecting T cells with antibody strategies.

B7-2 expression above a threshold elicits anti-tumor immunity as effective as interleukin-12 and prolongs survival in murine B-cell lymphoma

The costimulatory molecule, B7-2, is expressed by various lymphomas, but this level of expression is not sufficient to generate effective anti-tumor immunity in vivo. To determine whether up-regulated expression of the costimulatory molecule, B7-2, leads to more effective anti-tumor immunity in vivo, the A20 murine model of B-cell lymphoma was used. A20 tumor cells express major histocompatibility complex (MHC) I and II molecules and moderate constitutive levels of B7-2. While B7-1 and B7-2 have been introduced into tumor cells lacking these molecules, studies have not been conducted to determine whether tumors that constitutively express B7-1 or B7-2 can be made more immunogenic by increasing the expression of these molecules. In this report, A20/B7-2 transfectants expressing greater levels of B7-2 were rejected in syngeneic mice, and systemic immunity against the A20 parental cells was generated. Treatment with the A20/B7-2 variant cells significantly improved the survival of tumor-bearing mice. Coinjection with IL-12 secreting variants did not further augment the anti-tumor immunity observed for B7-2 therapy alone. Both CD8(+) T cells and natural killer (NK) cells mediated the anti-tumor immune response observed in A20/B7-2 immunized mice. In mice that developed tumors after immunization with the A20/B7-2 variant cells, resected tumor cells were shown to express lower levels of B7-2 than the transfected variants. These results suggest that the level of costimulation is important for the generation of anti-tumor immunity and for host survival. In addition, tumors appear to be able to evade the immune response by downregulating the expression of B7-2 below a threshold level.

Antitumor immunity after vaccination with B lymphoma cells overexpressing a triad of costimulatory molecules

BACKGROUND

The costimulatory molecules B7-1, intercellular adhesion molecule-1 (ICAM-1), and leukocyte function-associated antigen-3 (LFA-3) play pivotal roles in the activation of T cells. We investigated whether in vivo vaccination with lymphoma cells infected with a recombinant, nonreplicating fowlpox (FP) virus encoding this triad of costimulatory molecules (TRICOM) could stimulate lymphoma-specific immunity.

METHODS

TRICOM-infected A20 B lymphoma cells were analyzed for expression of B7-1, ICAM-1, and LFA-3. Mice (10 per group) were vaccinated with irradiated A20 cells infected with either the TRICOM vector or the wild-type FP virus (WT-FP), challenged with live A20 tumor cells, and followed for survival. Mice with established A20 tumors were also treated with irradiated TRICOM-infected A20 cells. Survival curves were compared with the log-rank statistic. The mechanism of the antitumor effect was studied by in vivo depletion of CD4(+) and CD8(+) T cells and in vitro cytotoxicity assays. All statistical tests were two-sided.

RESULTS

A20 tumor cells infected with TRICOM expressed high levels of B7-1, ICAM-1, and LFA-3. Mice vaccinated with irradiated TRICOM-infected A20 cells had prolonged survival relative to mice vaccinated with WT-FP-infected cells (80% versus 20% survival at 110 days; P<.001). In mice with established tumors, tumor growth was slower in those treated with TRICOM-infected tumor cells than in those treated with WT-FP-infected cells, and this treatment provided a survival advantage (P<.001). Depletion of CD4(+) or CD8(+) T cells reduced the antitumor immunity provided by the tumor cell-TRICOM vaccine, and lymphocytes from vaccinated mice displayed in vitro cytotoxic activity toward A20 cells.

CONCLUSIONS

Increasing expression of costimulatory molecules on B lymphoma cells by infection with a recombinant FP virus encoding B7-1, ICAM-1, and LFA-3 stimulates antitumor immune responses in vivo and may provide a novel strategy for treating patients with B-cell malignancies.

Dendritic cell-based immunotherapy for the treatment of hematological malignancies

Dendritic cells (DCs) are professional antigen-presenting cells and are frequently used in current immunotherapy protocols. The administration of DCs loaded with tumor-associated proteins or peptides results in the induction of immune responses against different types of malignant cells. Methods for large-scale generation of DCs in a sufficient quality and quantity have permitted their use in clinical experiments. DC-based vaccines have already shown promise in follicular non-Hodgkin's lymphoma, and to some extent, in other hematological malignancies. Several strategies have been developed to boost their potency as a new and relatively non-toxic treatment modality. Our review focuses on clinical trials using DCs in the treatment of hematologic malignancies and on recent studies of the immunophenotype, development, and maturation of DCs may have an important impact on designing DC-based antitumor vaccines.

T-cell analysis in identical twins reveals an impaired anti-follicular lymphoma immune response in the patient but not in the healthy twin

In lymphomas an innate defect in the T-cell repertoire could account for the impaired tumour-specific immune response; alternatively, the tumour itself could exert an inhibitory effect on the immune system. To address this issue we analysed the T-cell responses against follicular lymphoma (FL) in identical twins as it can be postulated that their overall T-cell repertoire is identical. While differences between the T-cell response of the patient and the healthy twin would point to a tumour-induced T-cell unresponsiveness, impaired responses in both would point to a defective T-cell repertoire. We demonstrated an impaired tumour-specific proliferation (P = 0.035 and P = 0.013) and cytokine release (P = 0.004 and P = 0.0008) of both peripheral blood and tumour-derived T-cells, respectively, in the FL patient compared with the T-cell response of the healthy twin. Moreover, only syngeneic primed T cells were able to directly lyse unmodified FL cells of the patient. These data support previous findings in murine lymphomas and suggest that inhibitory mechanisms during tumour growth, rather than a defective T-cell repertoire, are responsible for the insufficient T-cell response in lymphoma.