The augmentation of tumor-specific immunity by virus help. III. Enhanced generation of tumor-specific Lyt-1+2- T cells is responsible for augmented tumor immunity in vivo

Tumor cells treated with vaccinia virus can activate the alternative pathway of mouse complement

Vaccinia virus has been shown to render mouse tumor cells highly immunogenic. Since we have demonstrated that induction of complement activating capacity on guinea pig tumor cells by Sendai virus infection causes the tumor cells to become immunogenic, we assumed that vaccinia virus infection of mouse tumor cells might render them reactive with homologous mouse complement. Therefore, murine tumor cells, MH134 and X5563, infected with vaccinia virus (VV) were incubated with mouse plasma and C3 deposition was determined by staining with fluorescein isothiocyanate-labeled anti-C3. We found that VV-infected tumor cells possess the ability to activate the alternative complement pathway (ACP) of murine complement. For induction of complement activating ability, at least a 3 h incubation of the infected MH134 cells was required indicating that the generation of ACP-activating capacity on MH134 infected with VV is time-dependent. Furthermore, ultraviolet-irradiated vaccinia virus was able to induce ACP-activating capacity on tumor cells as well.

Modification of tumor cells by a low dose of Newcastle disease virus. II. Augmented tumor-specific T cell response as a result of CD4+ and CD8+ immune T cell cooperation

Augmented tumor-specific T cell responses were observed against the high metastatic murine lymphoma variant ESb when using as immunogen ESb tumor cells that had been modified by infection with a low dose of Newcastle disease virus (NDV). Such virus-modified inactivated tumor cells (ESb-NDV) were potent tumor vaccines when applied postoperatively for active specific immunotherapy of ESb metastases. We demonstrate here that immune spleen cells from mice immunized with ESb-NDV contain enhanced immune capacity in both the CD4+, CD8- and the CD4-, CD8+ T cell compartments to mount a secondary-tumor-specific cytotoxic T cell response in comparison with immune cells from mice immunized with ESb. ESb-NDV immune CD4+, CD8- helper T cells also produced more interleukin 2 after antigen stimulation than the corresponding ESb immune cells. There was no participation of either CD4+ or CD8+ virus-specific cells in the augmented response. The specificity of the T cells for the tumor-associated antigen remained unchanged. Thus, there is the paradox that the virus-mediated augmentation of the tumor-specific T cell response in this system involves increased T helper activity but does not involve the recognition of viral epitopes as potential new helper determinants.

Helper strategy in tumor immunology: expansion of helper lymphocytes and utilization of helper lymphokines for experimental and clinical immunotherapy

Two main kinds of immune strategy are possible against neoplasia. The first potentiates a selected effector arm. In vitro culture with exogenous interleukin-2 (IL-2) increases the activity of natural killer cells and leads to the expansion of T cytotoxic lymphocytes. Systemic reinfusion of both of these cells with high doses of IL-2 mediates the regression of a variety of murine and human tumors. In an alternative strategy, a few regulatory lymphocytes turn on immune reactivity by triggering a cascade of interconnected effector functions. The efficacy of this strategy rests on the repertoire of effector mechanisms moved to action. An effective immunoregulatory maneuver is the addition of helper determinants on the surface of tumor cells. Its power can be further increased by the pre-induction of helper T lymphocytes specific to the helper determinants. This approach can be achieved in mice by coupling muramyl dipeptides to tumor cells, along with eliciting T lymphocytes specifically reactive to Bacillus Calmette-Guerin. Noncytotoxic T helper lymphocytes produce factors which recruit nonspecific (macrophages) as well as specific (cytolytic T lymphocytes) anti-tumor attacking cells. In this way protection can be afforded against primary tumors and metastases, as well as leukemia cells. As the activity of helper lymphocytes rests mostly on lymphokine release, the use of molecularly defined lymphokines mimicking T-helper functions has also been attempted. In a few experimental models, the association of low doses of IL-2 with non-reactive lymphocytes from tumor-bearing mice promotes an effective anti-tumor reaction in the host. Moreover, the combination of distinct lymphokines can also build a molecularly defined helper system able to activate in sequence non-specific and specific anti-tumor reactions in vivo. Trials intended to evaluate the clinical impact of these helper approaches in the management of human tumors are being started or are already under way.

Establishment of tumor-specific immunotherapy model utilizing vaccinia virus-reactive helper T cell activity

It was previously demonstrated that preimmunization of mice with live vaccinia virus (VV) and subsequent immunization with VV-infected (modified), syngeneic tumor cells resulted in enhanced induction of tumor-specific immunity through a cellular collaboration between VV-reactive helper T (VV-Th) cells and tumor-specific effector cell precursors. On the basis of this augmenting system, a tumor-specific immunotherapy model was established in which a growing tumor regressed. C3H/HeN mice were pretreated with cyclophosphamide to eliminate nonspecific suppressor T cell activity and subsequently inoculated (primed) s.c. with live VV, leading to augmented induction of VV-Th cell activities. Four weeks later, the mice were inoculated i.d. with syngeneic X5563 myeloma cells. Six days after the tumor cell inoculation, live VV was injected into the tumor mass three times at 2-day intervals. Seven of ten mice which had received VV priming and subsequent VV injection into the tumor mass exhibited complete tumor regression. On the contrary, mice which had received mere intratumoral VV injection in the absence of VV priming failed to exhibit appreciable tumor regression. Mice whose tumor had completely regressed (regressor mice) by the above VV immunotherapy were shown to have acquired systemic anti-tumor immunity, which was confirmed by a challenge with syngeneic tumor cells after the tumor regression. In vitro analysis of these immune mice revealed that potent tumor-specific cytotoxic T lymphocyte responses were preferentially induced, but with no detectable anti-tumor antibody responses. Such a potent tumor-specific immunity was not observed in mice which had received an intratumoral VV injection in the absence of VV priming. Thus the results clearly indicate that the tumor regression was accompanied by concurrent generation of a potent tumor-specific immunity, suggesting that the cellular collaboration between VV-Th cells and tumor-specific effector cell precursors is also functioning in this VV-immunotherapy protocol, likewise the immunoprophylactic model. Therefore, the present model provides an effective maneuver for tumor-specific immunotherapy and this system will be theoretically applicable to human cancer treatment.

Immunotherapy of tumor-bearing mice utilizing virus help

Utilizing vaccinia virus (VV), a tumor-specific immunotherapy model was established in which a growing tumor regressed. C3H/HeN mice were primed with VV after low dose irradiation to generate amplified VV-reactive T cell activities. Then 4 weeks later, the mice were inoculated i.d. with syngeneic MH134 hepatoma cells, and 6 days after the tumor cell inoculation, live VV was injected into the tumor mass 3 times at 2-day intervals. Of 10 mice which had received VV priming and subsequent VV injection into the tumor mass, 8 exhibited complete tumor regression. On the contrary, mice which had received only intratumoral VV injection without VV priming failed to exhibit appreciable tumor regression. Mice whose tumor had completely regressed following the VV immunotherapy were shown to have acquired systemic antitumor immunity, which was confirmed by a challenge with syngeneic tumor cells after immunotherapy. In vitro analysis of these immune mice revealed that potent tumor-specific antibody responses were preferentially induced, but with no detectable antitumor cytotoxic T lymphocyte (CTL) responses. Such a potent tumor-specific immunity was not observed in mice which had received intratumoral VV injection in the absence of VV priming. Thus, the results clearly indicate that tumor regression was accompanied by the concurrent generation of a potent tumor-specific immunity, suggesting that cellular cooperation between VV-reactive T cells and tumor-specific effector cells might be functioning in this VV immunotherapy protocol. Therefore, the present model provides an effective maneuver for tumor-specific immunotherapy. This system is, in principle, applicable to the human situation.

Feasibility of UV-inactivated vaccinia virus in the modification of tumor cells for augmentation of their immunogenicity

We compared the immunity induced by tumor cells modified with UV-inactivated purified vaccinia virus (UV-VV) and with live purified vaccinia virus (L-VV). C3H/HeN mice were inoculated i.p. with UV-VV or L-VV after whole-body irradiation with 150 rads of X-rays (priming). After 3 weeks the mice were immunized i.p. 3 times at weekly intervals with syngeneic X5563 or MH134 cells that had been absorbed in vitro with UV-VV or infected with L-VV and subsequently irradiated with 10(4) rads of X-rays. Then 1 week after the last immunization, the mice were challenged s.c. with X5563 viable tumor cells or challenged i.p. with MH134 viable tumor cells. The 50% lethal dose (TLD50) of X5563 in mice primed and immunized with UV-VV (UV-VV group) on s.c. challenge (10(6.06)) was the same as for mice treated with L-VV (L-VV group), whereas the TLD50 of unprimed or nonimmunized mice (control group) was 10(2.61). The TLD50 of MH134 in the UV-VV treated group on i.p. challenge (10(6.48)) was similar to that of the L-VV treated group (10(6.54)), while the TLD50 of the control group was 10(1.00). The difference between the TLD50 values of X5563 on s.c. challenge of mice primed and immunized with UV-VV or L-VV and control mice was 10(3.4). The difference between the TLD50 values of MH134 on i.p. challenge of primed and immunized mice and control mice was 10(5.5). These results indicate that the in vivo helper function of UV-VV is similar to that of L-VV and that the augmenting effect of this protocol depends on the kind of tumor.