Generation of cytotoxic antibodies to the B16 murine melanoma using a formalinized vaccine

Formalin-fixed tumor cells effectively induce antitumor immunity both in prophylactic and therapeutic conditions

BACKGROUND

Autologous whole tumor cell-based vaccinations would seem to be ideal since such vaccinations, in contrast to vaccination with a single defined antigen, have the potential to elicit a broad type of T-cell immune response to tumor-associated antigens.

OBJECTIVE

We modified formaldehyde (formalin)-fixed mouse melanoma cells and investigated the utility of those cells as sources of tumor antigens for immunotherapy.

METHODS

C57BL/6 or the proteasome activator PA28alpha-knockout mice were intradermally inoculated with 1% formalin-fixed B16 cells three times at weekly intervals either before or after tumor challenge. Simultaneously, interleukin-12 gene was transferred into the skin around immunization sites using gene gun technology. The effects were evaluated by tumor growth, antigen-specific interferon-gamma production in splenic lymphocytes, and activation of dendritic cells.

RESULTS

Fixed cells directly induced production of tumor necrosis factor-alpha in dendritic cells more effectively than did frozen and thawed cells. More than 60% of the mice immunized with fixed cells and interleukin-12 rejected the challenged B16 tumor. CD4+ T cells from those mice produced a significant amount of interferon-gamma in response to melanoma cells. Furthermore, this combined treatment showed antitumor immunity initiated by CD8+ and CD4+ T cells in the therapeutic experiments. PA28alpha/beta appeared not to be required for the development of CD8+ T cells, although it is known to be essential for the development of CD8+ T cells specific for tyrosinase-related protein-2, one of melanocyte-lineage differentiated antigens.

CONCLUSION

These results suggest that formalin-fixed autologous melanoma cells have a potential to function as effective antigen sources for immunotherapy.

Synergistic effect of interleukin-2 and a vaccine of irradiated melanoma cells transfected to secrete staphylococcal enterotoxin A

We have previously reported that immunization of mice with melanoma cells transfected to secrete the superantigen, Staphylococcal enterotoxin A (SEA), increased the production of antibodies to the B700 melanoma antigen, stimulated the production of endogenous interleukin 2 (IL-2), activated the expression of CD4, CD8 and CD25 T cell markers and enhanced NK cell activity. Now we show that immunization of mice with a vaccine of irradiated sea-transfected melanoma cells coupled with IL-2 therapy was even more effective in inhibiting the growth of primary melanoma tumors and the development of lung metastases than was the irradiated melanoma cell vaccine alone or IL-2 alone. The morphological and immunological effectiveness of the therapy was dose-dependent on IL-2.

Capacity of murine IL-12 to inhibit the development of primary melanoma tumors and to prevent lung metastases in the melanoma-challenged mice

Interleukin-12 (IL-12) has the capacity to activate cytotoxic lymphocytes, stimulate natural killer cells, induce the production of INF-gamma, and be synergistic with IL-2. We have evaluated this cytokine in an experimental model for metastatic melanoma that approximates the major clinical stages of metastatic dissemination. To develop primary melanoma tumors, mice were injected subcutaneously with 5 x 10(5) cells in a volume of 25 microliters into the middle of the tail (11). In a month, mice were started to be treated for 4 weeks with recombinant murine IL-12 (R mIL-12) at the following doses: 0, 0.5, 2.5, 5.0, 15.0, and 50 micrograms/kg. Diameters of the primary melanoma tumors were measured at weekly intervals. At the end of 13 weeks (9 weeks from the start of treatment with R mIL-12), all surviving mice were sacrificed. Pathological examination of lung metastases (macroscopy) was done with all dead or sacrificed mice. Treatment of mice bearing melanoma at a dose of 300 ng/mouse (15 micrograms/kg) inhibited development of primary tumors in 40% of mice. The primary tumor diameters were significantly lower in the group treated with 300 ng/mouse (15 micrograms/kg) in comparison to controls. At the end of the observation period, groups treated with 0.5, 2.5, 15.0, and 50 micrograms/kg had mean primary tumor diameters smaller than the control group. Evaluation of IL-12 therapy on primary tumor growth, mean diameters of primary tumors, survival rate, and development of lung metastases showed that the best results were observed using 300 ng/mouse (15 micrograms/kg) R mIL-12.

Immunotherapy of mice with an irradiated melanoma vaccine coupled with interleukin-12

Interleukin (IL)-12 can activate cytotoxic lymphocytes, stimulate natural killer cell activity, induce the production of INF-gamma and inhibit the development of various experimental tumors. We previously demonstrated that immunotherapy of melanoma bearing mice with an irradiated melanoma vaccine (IMV) coupled with IL-2 or GM-CSF had beneficial effects against primary melanoma growth and against subsequent spontaneous metastasis. We also had found that treatment of melanoma bearing mice with IL-12 (300 ng/day) for 4 weeks inhibited the development of primary melanoma tumors in 40% of mice. The purpose of this study was to investigate the efficacy of combined therapy of experimental melanoma with an IMV prepared from B16F10 melanoma cells coupled with IL-12 treatment. C57BL/6 mice were challenged subcutaneously in the tail with B16F10 melanoma cells and by the 45th day, more than 50% of the mice had developed visible primary melanoma tumors at the injection site. Subsequent immunotherapy of mice with IMV, when coupled with IL-12, provided partial inhibition of primary melanoma tumor growth. Optimal results against primary tumor growth were observed when IMV therapy was coupled with IL-12 at a dose of 50 ng/day. Combination of IMV with IL-12 at a dose of 100 ng/day significantly reduced melanoma metastasis to the lungs compared with control mice, and an improvement in mean survival time was observed in mice treated with a combination of IMV with IL-12 (300 ng/day).

Immuno-protective effect of tumor cell vaccine on Kunming mice bearing Ehrlich ascites tumor

AIM: To evaluate the immunity of chemically modified tumor cell vaccine.

METHODS: Tumor cell vaccines (TCV) were prepared by incubating the live Ehrlich ascites tumor cells with concanavalin A-mitomycin C (ConA-MMC), mitomycin C (MMC), concanavalin A-glutaraldehyde (ConA-Glu), glutaraldehyde ( Glu ), or paraformaldehyde ( Para ), respectively. The whole cell or soluble forms of the vaccines were administered intraperitoneally into Kunming mice once a week for three times prior to the intraperitoneal inoculation of a lethal dose of live tumor cells. A second challenge with live tumor cells was given four weeks later. Survival and antibody production of the mice were analyzed.

RESULTS: After the first challenge, the mice, received whole TCV of ConA-MMC, MMC (P < 0.01) and Glu (P < 0.05) promoted survival incidence than the controls. All the treated mice had the survival time prolonged. ConA-MMC vaccine treated mice had longer survival days than that of ConA-Glu ones (P < 0.05). For the soluble TCV immunized mice, those treated with vaccines of Para (P < 0.01), ConA-Para and ConA-Glu (P < 0.05) had longer survival periods compared with that of the controls. Following the second challenge, survival incidence of the mice received vaccines of ConA-MMC, MMC, ConA-Glu or Glu was significantly increased (P < 0.01). Moreover, all the treated mice had the survival time prolonged, and ConA-MMC vaccine treated mice had longer survival days than that of Para treated ones (P < 0.05). Antibodies against Ehrlich ascites tumor cells were found to be positive in sera of the mice treated with whole TCV of ConA-MMC.

CONCLUSION: Ehrlich ascites tumor cells are immunogenic when treated with ConA-MMC, MMC, ConA-Glu, Glu or Para, which might act as safe and effective tumor vaccines with safety and effectiveness.

Further characterization of a clinically relevant model of melanoma metastasis and an effective vaccine

A major problem in evaluating the effectiveness of tumor cell vaccination and other biological therapies is the variability of experimental models. In this study we have further developed and characterized a model for metastatic melanoma that approximates the major clinical stages of metastatic dissemination: stage I--growth of the primary (local) tumor, stage II--dissemination to regional lymph nodes, and stage III--metastasis to distant organs (lungs). C57BL/6 mice were challenged subcutaneously with B16 F10 murine melanoma cells in the midtail, and within 3 weeks 100% of the mice had local tumors growing in their tails. By 5-7 weeks after challenge, most of the mice had developed metastases to the inguinal lymph nodes and subsequently had metastatic colonies in the lungs and in the bone marrow. Preimmunization of mice with a formalinized extracellular antigen vaccine, derived from B16 F10 melanoma cells, provided partial inhibition of the growth of the primary melanoma tumors, as well as reducing the number of metastases to the regional (inguinal) lymph nodes and lungs along with concomitantly increasing survival time. This model for melanoma metastasis provides a reasonable and reproducible test system for the study of anti-melanoma immunity and the different cellular and humoral mechanisms involved.

Novel experimental approaches to melanoma diagnosis and therapy

We have investigated the potential use of immune therapies on the growth of melanoma metastases in a new animal model that more closely approximates the clinical situation. We have found that significant benefits towards decreased metastatic growth and subsequent animal survival can be achieved by treatment of tumor-bearing mice with melanoma-specific monoclonal antibodies or alternatively, with various types of monovalent or polyvalent vaccines. The beneficial effects of those vaccines can be significantly enhanced by concomitant interleukin-2 therapy.

Nude mouse model to study passive humoral immunotherapy directed against B16 F10 murine melanoma

A model to study passive humoral immunotherapy of experimental melanoma was generated by subcutaneous injection of B16 F10 murine melanoma cells in the midtail of BALB/C nude (nu/nu) mice. Mice were challenged with melanoma cells pretreated: (1) with complete culture medium, (2) with 10% adjuvant control serum, (3) with 10% anti-fECA (formalinized extracellular antigens) immune serum, or (4) with a monoclonal antibody (mAB H2-3-3) specific for the B700 melanoma-associated antigen. All control mice challenged with melanoma cells pretreated either with culture medium or with medium containing adjuvant control serum (Groups I and II) died during the observation period of 84 days. At day 84, 60% of the mice challenged with melanoma cells pretreated with anti-fECA immune serum (Group III) survived, as did 100% of the mice challenged with cells pretreated with mAb H2-3-3 (Group IV). Injection of melanoma cells pretreated with mAb H2-3-3 was associated with the greatest reduction of subsequent local tumor growth and the lowest number of metastatic lung tumors. The inhibitory effects of immune sera in vivo also correlated with in vitro effects of anti-fECA immune serum and mAb H2-3-3, determined on B16 F10 melanoma target cells using assays for DNA synthesis and antibody dependent cellular cytotoxicity (ADCC). In sum, this nude mouse model for the study of passive humoral immunotherapy of experimental melanoma was utilized to demonstrate significant protective effects against B16 F10 melanoma cell challenge by treatment with anti-fECA immune sera or a melanoma-specific monoclonal antibody.

Further studies of the therapeutic effects of murine melanoma-specific monoclonal antibodies

The results presented here further characterize four murine monoclonal antibodies (mAb) that recognize melanoma-specific antigens (9B6, T97, 2-3-1 and 2-3-3). These melanoma-specific mAbs are of the IgG2b isotype and are significantly therapeutic when administered systemically against established pulmonary melanoma metastases. Here we show a consistent and significant inhibition of the growth of melanoma lung metastases by all four mAbs and the existence of a time 'window' at days 5-8 after tumor inoculation for optimal therapy. Since these mAbs were found not to be cytotoxic or cytolytic in vitro, we looked for host immune response regulation as being responsible for the therapeutic effects. Natural killer (NK) cells were implicated as one arm of the host immune system involved in this response since depletion of NK cells in vivo by alpha asialoGM1 or alpha NK1.1 antibodies partially abrogated the inhibitory effect of the mAbs. The observed antimetastatic effects could also be partially abrogated using antibodies directed against the T-cell subset surface markers, CD4+ and CD8+. Intramuscular melanoma tumor growth was also found to be suppressed by mAb 2-3-1, but only if administered in the area of tumor growth and only if multiple inoculations are administered over a 13-day period. The beneficial effect of mAb antimetastatic therapy was found to be useful against several syngeneic melanomas, including JB/MS, B16 and several sublines of the B16 F10 melanoma.