Abstract
The interaction between CD40 and CD40 ligand (CD40L) on antigen presenting cells (APC) is critical in promoting cellular immune responses. In vitro experiments have shown that lymphoma B cells are efficiently infected by virus vectors encoding CD40L and subsequently up-regulate co-stimulatory molecules. By infection with CD40L, lymphoma B cells could function as APC. Tumor cells modified ex vivo to express CD40L have been shown to be able to induce protective immunity against subsequent tumor challenge. In order to develop an immunotherapy approach against established tumor, we tested the effect of intratumor injection of the recombinant fowlpox virus encoding murine CD40L (rF-mCD40L) together with systemic administration of cyclophosphamide (CTX). Methods: BALB/C mice were first inoculated s.c. with 1×107 syngeneic A20 lymphoma cells. On day 15, when tumor reached approximately 1.0 cm in diameter, mice were separated into 6 groups of ten mice which received: 1) rF-mCD40L alone, 2) empty fowlpox virus (FP-virus) alone, 3) PBS, 4) CTX (100mg/kg, i.p), 5) rF-mCD40L plus CTX, 6) FP-virus plus CTX. Virus was administrated twice by intratumoral injection at a dose of 1×109 pfu at a 7 days interval. CTX was delivered i.p at a dose of 100mg/kg on two successive days between the two virus injections. Tumor growth and animal survival were monitored every three days. In addition, tumor cell transgene expression was measured by flow cytometry 24 hours following virus injection. Results: After 24 hours of intratumor injection, a small percentage of tumor cells shown to be positive for the transgene on analysis. As shown in Figure 1, Chemotherapy alone caused only temporary regression of tumor, but the combination of rF-mCD40L with CTX resulted in tumor free mice 80 days after tumor inoculation. By contrast, mice treated with rF-mCD40L alone or with empty virus, died 4 to 7 weeks after tumor inoculation. 40 to 50% of mice treated with CTX alone or with FP virus combined with CTX exhibited re-occurrence of tumor growth and 3 mice in group of CTX alone, 2 mice in the group of FP virus combined with CTX died of tumor progression. Conclusion: rF-mCD40L alone had no anti-tumor effect against established lymphoma. Intratumor injection of rF-mCD40L in combination with systemic chemotherapy was effective for the therapy of advanced lymphoma. Intratumor administration of CD40L in combination with chemotherapy may be a promising strategy for the treatment of advanced lymphoma.
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