Eradication of a large MOPC-315 tumor in athymic nude mice by chemoimmunotherapy with Lyt2+ splenic T cells from melphalan-treated BALB/c mice bearing a large MOPC-315 tumor

Chemo-immunotherapy and chemo-adoptive immunotherapy of cancer

The chemo-immunotherapy (CIT) and chemo-adoptive immunotherapy (CAIT) regimens tested in the past decade are summarized. From them we have learned a great deal about the interactions between various chemotherapeutic agents, immune modulating agents and effector cells. The most commonly reported result in multi-modality experiments with CAIT has been a synergistic enhancement in antitumor activity. Clinical trials usually demonstrated improvement in patient quality of life, an extension of survival time, and occasional complete regression of tumor. In many animal models, this enhancement often meant the complete regression and apparent cure of tumor in the animal. One mechanism by which this synergistic enhancement takes place appears to be a suppression of tumor-associated suppressor T cell activity by the chemotherapeutic agents, thereby inducing enhanced cytolytic activity against tumor by the adoptively transferred, activated effector cells. In CAIT the most commonly used drug has been cyclophosphamide. In CIT a wide variety of chemotherapy agents have been used but none of the clinical trials made use of cyclophosphamide. Thus, direct comparisons are not possible. Suggestive of the intricate regulatory processes involved, many CIT studies indicate a synergy only when specific doses of chemotherapy and immunotherapy agents are given, and in a specific sequence. CIT has become less toxic, is being handled on a cost-effective outpatient basis, while maintaining similar objective response rates to earlier inpatient treatments. In the future, CAIT and CIT will probably have an increasing role in the management of patients with specific cancers.

Transforming growth factor-beta-mediated down-regulation of antitumor cytotoxicity of spleen cells from MOPC-315 tumor-bearing mice engaged in tumor eradication following low-dose melphalan therapy

We have previously shown that treatment of mice bearing a large MOPC-315 plasmacytoma with a low dose of the anticancer drug melphalan (L-phenylalanine mustard; L-PAM) results in the acquisition of a potent CD8+ T-cell-mediated anti-MOPC-315 cytotoxic T lymphocyte (CTL) activity by the hitherto immunosuppressed tumor bearers, and this immunity contributes to complete tumor eradication. In the studies presented here, we sought to determine how the acquisition of this antitumor immunity following low-dose chemotherapy is possible, in light of the report that MOPC-315 tumor cells produce transforming growth factor-beta (TGF-beta), an immunosuppressive cytokine that can down-regulate the generation of CTL responses. We found that the acquisition of CTL activity following low-dose L-PAM therapy is not due to a chemotherapy-induced decrease in the sensitivity of MOPC-315 tumor bearer spleen cells to TGF-beta-mediated inhibition of CTL generation. Moreover, even spleen cells from MOPC-315 tumor-bearing mice, which had received L-PAM therapy 7 days earlier and had acquired CTL activity in vivo, were sensitive to the inhibitory activity of TGF-beta upon culture for as little as 1 day, with or without stimulator tumor cells. However, the production of TGF-beta by MOPC-315 tumors decreased drastically as a consequence of the low-dose chemotherapy. Thus, the curative effectiveness of low-dose L-PAM therapy for MOPC-315 tumor-bearing mice may be due, at least in part, to a reduction in TGF-beta production that enables the development of tumor-eradicating immunity.

Cure of mice bearing a late-stage, highly metastatic, drug-resistant tumor by adoptive chemoimmunotherapy

We show here that in contrast to BALB/c mice bearing a late-stage, large MOPC-315 plasmacytoma, BALB/c mice bearing a late-stage, large RPC-5 plasmacytoma were not cured by cyclophosphamide therapy (15, 50, 100 or 200 mg/kg). However, most BALB/c mice bearing a late-stage RPC-5 tumor were cured by cyclophosphamide therapy (100 mg/kg) in conjunction with adoptive immunotherapy using tumor-infiltrated spleen cells (TISpC) that had been cultured with inactivated RPC-5 tumor cells plus polyethylene glycol 6000, even though this protocol was not effective for the therapy of mice bearing a barely palpable, early-stage RPC-5 tumor. Only a few of the mice that were cured of a late-stage RPC-5 tumor following adoptive chemoimmunotherapy (ACIT) were resistant to a subsequent challenge with RPC-5 tumor cells. However, the challenged mice that had developed progressively growing tumors could then be cured by cyclophosphamide alone when the tumor became large, even though this treatment was not curative for mice bearing a tumor of similar size but not previously treated by ACIT. Thus, the cure by ACIT of BALB/c mice bearing a lethal, late-stage RPC-5 tumor with extensive metastases provides a novel experimental tumor model for investigating the mechanisms by which a chemotherapeutic drug and adoptive cellular immunotherapy can cooperate in causing the complete regression of a large tumor load.

Some approaches to improve the therapeutic effectiveness of adoptive chemoimmunotherapy with spleen cells from melphalan-treated BALB/c mice bearing a large MOPC-315 tumor

Spleen cells from BALB/c mice that are in the process of eradicating a large MOPC-315 tumor following low-dose L-PAM therapy (L-PAM TuB spleen cells) were previously shown to be capable of bringing about the complete regression of a large (15 to 20 mm) s.c. MOPC-315 tumor in a substantial percentage of T-cell-deficient (athymic nude) mice that had been treated with low-dose L-PAM (adoptive chemo-immunotherapy; ACIT). Here we show that aggressive depletion of CD4+T-cells by treatment both of spleen-cell donors and of recipients with anti-L3T4 monoclonal antibody (MAb) greatly improved the therapeutic effectiveness of L-PAM TuB spleen cells in ACIT. In the light of the apparent importance of cytotoxic T-lymphocytes (CTLs) for tumor eradication in low-dose L-PAM-treated MOPC-315-tumor bearers, it is interesting that treatment of L-PAM TuB spleen-cell donors with anti-L3T4 MAb was found to result in the generation of enhanced splenic anti-MOPC-315 cytotoxicity. Although most athymic nude mice in which the tumor had apparently completely regressed following ACIT remained tumor-free, approximately 1/3 of the mice relapsed. However, a substantial percentage of the relapsing mice were rescued by a low dose of L-PAM, which was not effective in causing tumor regression in athymic nude mice bearing a comparably large tumor if the mice had not been subjected previously to ACIT. Almost all athymic nude mice that had been "cured" of a large MOPC-315 tumor by ACIT but did not resist a subsequent MOPC-315 tumor challenge were rescued by low dose L-PAM. Thus, the therapeutic effectiveness of L-PAM TuB spleen cells in ACIT may be improved by aggressive depletion of CD4+ T-cells, suggesting that a low dose of L-PAM, which leads to the acquisition of potent splenic-tumor-eradicating immunity in BALB/c mice bearing a large MOPC-315 tumor, does not eliminate completely (or possibly not at all) the inhibitory activity of CD4+ T-cells. In addition, athymic nude mice that are not endowed with fully protective tumor-eradicating immunity following ACIT still have a substantial residual anti-tumor immune potential that can be exploited to bring about eradication of a large tumor burden following low-dose L-PAM therapy.

Phorbol ester-induced enhancement in lytic activity of CD8+ splenic T cells from low-dose melphalan-treated MOPC-315-tumor bearers

We have previously shown that while spleen cells from untreated mice bearing a large MOPC-315 tumor are not cytotoxic in vitro for MOPC-315 tumor cells, spleen cells obtained from such mice on day 7 after low-dose melphalan (L-phenylalanine mustard); L-PAM therapy exert a substantial anti-MOPC-315 cytotoxicity [Mokyr et al. (1989) Cancer Res 49: 4597]. Here we show that this anti-MOPC-315 lytic activity is evident by day 5, and peaks on day 7 after the low-dose chemotherapy, at a time when the mice are actively engaged in tumor eradication. Short-term exposure of spleen cells from mice bearing a MOPC-315 tumor and treated with low-dose L-PAM (L-PAM TuB mice) to phorbol 12-myristate 13-acetate (PMA) was found to enhance greatly the ability of these spleen cells to lyse MOPC-315 tumor cells. The highest level of anti-MOPC-315 cytotoxicity was obtained when spleen cells from tumor-bearing mice that had received chemotherapy 7 days earlier were exposed to PMA at a concentration of 1-10 ng/ml. The exertion of the enhanced anti-MOPC-315 lytic activity by L-PAM TuB spleen cells exposed to PMA was found to require CD8+, but not CD4+, T cells. The apparent specificity of the lytic activity exerted by the PMA-stimulated L-PAM TuB spleen cells was illustrated not only by the inability of the spleen cells to lyse an allogeneic, antigenically unrelated thymoma (EL4), but also by their relatively weak lytic activity for two antigenically related syngeneic plasmacytomas. In addition, when EL4 target cells were admixed with MOPC-315 tumor cells, the lytic activity triggered in the L-PAM TuB spleen cells by the MOPC-315 tumor cells plus PMA was not effective in lysing the antigenically unrelated target cells. Moreover, even in the presence of the calcium-specific ionophore, ionomycin, L-PAM TuB spleen cells exposed to PMA were unable to lyse the EL4 target cells. Thus, fresh CD8+ splenic T cells from L-PAM TuB mice that are in the process of eradicating a large MOPC-315 tumor as a consequence of low-dose L-PAM therapy can be triggered with PMA to exert enhanced lytic activity against MOPC-315 tumor cells.(ABSTRACT TRUNCATED AT 400 WORDS)