Retro virus-Mediated Gene Transfer of B7-1 and MHC Class II Converts a Poorly Immunogenic Neuroblastoma into a Highly Immunogenic One

Abstract

The T cell co-stimulatory molecule B7-1 was transduced into a poorly immunogenic murine neuroblastoma cell line (Neuro-2a, N-2a) alone or in combination with MHC class II genes to test the ability of these genes to stimulate antitumor immunity. N-2a cells transduced with B7-1 exhibited reduced tumorigenicity, whereas N-2a cells overexpressing both MHC class II (syngeneic, I-A^k) and B7-1 totally abrogated tumorigenicity. Rejection of I-A^k/B7-1 cells was dependent on both CD4⁺ and CD8⁺ T cells. The ability of both vaccines to induce protection against parental N-2a was temporally dependent on the time of secondary N-2a challenge. To investigate the immunity generated by N-2a/B7-1 and N-2a/I-A^k/B7-1 vaccines, we tested the ability of these modified cells to stimulate in vitro the proliferation of syngeneic splenocytes from naive mice. A significant increase in splenocyte proliferation was observed with N-2a/I-A^k/B7-1 cells compared to N-2a cells. We also determined that vaccination with N-2a/I-A^k/B7-1 cells was able to generate cytotoxic T cell responses to unmodified N-2a cells. The introduction of B7-1 and I-A^k into N-2a was able to convert a poorly immunogenic tumor to a highly immunogenic one; however, mice bearing large established unmodified tumors had little response to vaccination with N-2a/I-A^k/B7-1 cells. Our results emphasize the importance of tumor immunogenicity in the treatment of established tumors with MHC class II/B7-1 tumor cell vaccines.

Overview summary

The main goal of cancer immunotherapy is to find treatments that effectively recruit tumor-specific effector T cells to destroy tumors and generate long-lasting immunity. Modification of tumor cells to express T cell stimulatory genes represents an effective method of stimulating tumor immunity that may be applicable to the treatment of human cancer. In the experiments described here, the introduction of I-A^k and the T cell co-stimulatory molecule B7-1 into a murine neuroblastoma through retrovirus-mediated gene transfer abrogated tumorigenicity and established immunity, yet failed to prolong significantly the survival of mice bearing large wild-type tumors. The data suggest that transduction of poorly immunogenic tumor cells with MHC class II and B7-1 promotes a strong antitumor immune response through recruitment of both CD4⁺ and CD8⁺ T cells, thus bypassing professional antigen-presenting cells (APCs).