OBJECTIVETo test whether vaccination performed during irradiation or chemotherapeutics-induced lymphopenia-driven T cell proliferation could augment the antitumor immunity.

METHODSThe study composed of two parts, investigating the anti-tumor efficacy of performing tumor vaccination during early immune reconstitution period following sublethal total body irradiation and cyclophosphamide (Cy)-induced lymphopenia, respectively. Mice were subsequently reconstituted with naïve splenocytes from syngeneic mice and were named RLM (Reconstituted lymphopenic mice). Immunization/vaccination (F10) and adoptive immunotherapy (D5-G6) were used to explore anti-tumor immune responses in vaccinated irradiation/RLM and vaccinated Cy/RLM, respectively. Both normal C57BL/6 mice and RLM were vaccinated with irradiated, weakly immunogenic F10 melanoma cells and subsequently challenged with F10 cells. In addition, to determine the role of CD4(+) and CD8(+) T cells in the protective anti-tumor immune response, irradiation/RLM were depleted of these subpopulations by administration of the appropriate mAb around challenge. In the second part, adoptive immunotherapy was used to evaluate the anti-tumor immune responses under chemotherapeutics-induced lymphopenic condition. Both normal mice and RLM (Cy-treated) were vaccinated with GM-CSF-modified D5 melanoma cells (D5-G6) and tumor vaccine draining lymph nodes (TVDLN) were harvested 9-10 days later. Effector T cells were generated in vitro from TVDLN cells and adoptively transferred to mice bearing 3-day pre-established pulmonary metastases (D5). Recipient mice were sacrificed 2 weeks later after tumor inoculation and pulmonary metastases were enumerated.

RESULTSSignificantly greater protection was induced in vaccinated irradiation/RLM, compared to vaccinated normal mice (63.2% vs 16.7%). Protective immunity in RLM depended on CD8(+) T cells. Increase in the interval between reconstitution and vaccination significantly decrease the protection. Effector T cells generated from vaccinated Cy-treated RLM demonstrated significantly higher in vivo anti-tumor efficacy over those of vaccinated normal mice.

CONCLUSIONThis study suggests that vaccination of RLM could elicit augmented antitumor immunity compared to normal hosts, highlighting the potential clinical benefit of performing tumor vaccination during irradiation or chemotherapeutics-induced lymphopenia in cancer patients.

Animals ; CD8-Positive T-Lymphocytes ; immunology ; Cancer Vaccines ; therapeutic use ; Cyclophosphamide ; adverse effects ; Female ; Granulocyte-Macrophage Colony-Stimulating Factor ; immunology ; Immunotherapy, Adoptive ; methods ; Lymphopenia ; etiology ; therapy ; Melanoma, Experimental ; drug therapy ; immunology ; radiotherapy ; Mice ; Mice, Inbred C57BL ; Whole-Body Irradiation

OBJECTIVETo explore mechanisms of the augmented anti-tumor immunity observed in reconstituted lymphopenic mice (RLM) receiving melanoma vaccination.

METHODSThe study is to investigate the anti-tumor immunity of tumor vaccination during early immune reconstitution period following irradiation and cyclophosphamide (CY)-induced lymphopenia. Lymphopenic mice were subsequently reconstituted with naive splenocytes from syngeneic mice and immunized with irradiated melanoma cells F10 (irradiation experiment) and GM-CSF-modified D5 melanoma cells (D5-G6) (CY experiment). Controls included normal C57BL/6 mice receiving the corresponding vaccination, un-immunized naive mice and RLM. 8 - 10 days after vaccination, tumor vaccine draining lymph nodes (TVDLN) were harvested and phenotyped by FACS analysis. T cells purified from TVDLN were stimulated with anti-CD3 and anti-TCRbeta and proliferation was assessed by [(3)H]-TdR incorporation and FACS assay was performed for CD69 expression.

RESULTSThe augmented anti-tumor immunity correlated with a significant increase in the percentage of T cells with activation/memory phenotype in the TVDLN of vaccinated RLM, compared to that of the controls. There was also a significant increase in the density of DCs in TVDLNs. The activation threshold of T cells generated from vaccinated RLM was significantly decreased, resulting in markedly enhanced proliferating capability upon anti-CD3 stimulation.

CONCLUSIONThis study suggests that the augmented anti-tumor immunity observed in vaccinated RLM is due to down regulated activation threshold of T cells during lymphopenia-driven T cell proliferation, which may in turn facilitate the breaking down of immune tolerance to weak tumor antigens upon vaccination with tumor cell vaccines.

Animals ; Cancer Vaccines ; administration & dosage ; Cyclophosphamide ; Lymph Nodes ; immunology ; Lymphopenia ; etiology ; immunology ; Male ; Melanoma, Experimental ; immunology ; therapy ; Mice ; Mice, Inbred C57BL ; T-Lymphocytes ; immunology ; Whole-Body Irradiation