Adoptive transfer of anti-CD3-activated CD4⁺ T cells plus cyclophosphamide and liposome-encapsulated interleukin-2 cure murine MC-38 and 3LL tumors and establish tumor-specific immunity

The infusion of anti-CD3-activated murine T cells plus interleukin-2 (IL-2) exerts antitumor effects against several tumors in murine immunotherapy models. This study compares the therapeutic efficacy of anti- CD3-activated CD4⁺ or CD8⁺ T-cell subsets, when given with cyclophosphamide (Cy) and liposome-encapsulated IL-2 (L-IL2) in a murine model. C57BL/6 mice bearing subcutaneous (SC) MC-38 colon adenocarcinoma, 3LL Lewis lung carcinoma, or 38C13 lymphoma for 7 to 14 days were pretreated with low-dose intraperitoneal (IP) Cy before intravenous (IV) injection of anti-CD3- activated T cells or T-cell subsets. Cell administration was followed by IP administration of L-IL2 for 5 days. Mice receiving activated CD4⁺ T cells showed significantly reduced tumor growth or complete remissions with prolonged disease-free survival in MC-38, 3LL, and 38C13. The timing of Cy doses in relation to adoptive transfer was critical in obtaining the optimal antitumor effect by CD4⁺ cells. Injecting Cy 4 days before the infusion of CD4⁺ cells greatly enhanced the antitumor effect of the CD4⁺ cells and improved survival of the mice compared with other Cy regimens. C57BL/6 mice cured of MC-38 after treatment with CD4⁺ T cells developed tumor-type immunologic memory as demonstrated by their ability to reject rechallenges with MC-38, but not 3LL. Similarly, mice cured of 3LL tumors rejected rechallenges of 3LL, but not MC-38. The immunologic memory could be transferred with an IV injection of splenocytes from mice cured of MC-38 or 3LL. No cytotoxic T-lymphocyte activity was detected in T cells or T-cell subsets from mice cured of MC-38 or 3LL. Increased IL-2 and interferon-γ, (IFN-γ) production was observed from CD4⁺ subsets in cured animals when stimulated in vitro with the original tumor, but not with an unrelated syngeneic tumor. These results suggest that tumor-specific immunity can be achieved in vivo with anti-CD3-stimulated CD4⁺ T cells in this cellular therapy model.