Abstract
Individuals of advanced chronological age exhibit an impaired immune response to vaccines. This may be due to a reduction in the ratio of antigen naïve/memory CD4 and CD8 T cells and acquisition of functional defects in activated “helper” CD4 T cells (eg diminished CD40 ligand (CD40L) expression) during the aging process. The absence of the CD40L on activated CD4 helper T cells reduces the magnitude of expansion of antigen specific T and B cells induced by vaccination. In order to circumvent this defective response to vaccines among individuals in the fifth and sixth decades of life, our laboratory has developed an adenoviral vector (Ad-sig-TAA/ecdCD40L) vaccine which is designed to overcome the absence of CD40L expression in activated CD4 helper T cells in older individuals. The subcutaneous (sc) injection of this vector leads to the release of a fusion protein composed of a TAA linked to the extracellular domain (ecd) of the CD40L, which binds to the CD40 receptor on DCs, activates the DCs, and leads to the presentation of TAA fragments on Class I MHC. Two sc injections of the TAA/ecdCD40L protein as a booster following the sc administration of the Ad-sig-TAA/ecdCD40L vector (we call this the TAA/ecdCD40L VPP vaccine) expands the magnitude of the cellular and humoral immune response induced by the vector in 18 month old aged mice as well as in younger mice. In order to explore ways of further amplifying the immune response induced by this vaccine, we decided to test the feasibility of using this vaccine following treatments which reduce the number of T cells in the body of the test subject. We hypothesized that during states of chemotherapy or radiation induced lymphopenia, the number of negative regulatory CD4CD25FoxP3 T cells would be reduced, and all of the regulatory signals in the T cell compartment would be promoting expansion of T cells, thus creating an ideal state for vaccination. To test this hypothesis, we injected 100,000 cells from an established neoplastic cell line sc. Three days later, we administered myeloablative doses of total body irradiation (TBI) followed by a T cell depleted syngeneic bone marrow transplant (TCDBMT) to reconstitute neutrophil and platelet production. Three days following the TBI and TCDBMT, we intravenously infused donor lymphocytes (DLI) from a TAA/ ecdCD40L VPP vaccinated syngeneic donor. Four weeks later, we vaccinated the recipient mouse further with TAA/ecdCD40L sc injections. We tested this for a TAA composed of a junctional peptide from the p210Bcr-Abl protein of chronic myelogenous leukemia (CML) and for the E7 protein of the human papilloma virus (HPV). We found that in the case of the BcrAbl/ecdCD40L VPP vaccine, 50% of the mice treated with TBI, TCDBMT, ten million lymphocytes (DLI) from BcrAbl/ecdCD40L VPP vaccinated syngeneic donors followed in 4 weeks by 3 BcrAbl/ecdCD40L protein sc injections of the recipient test mouse, developed a complete response with the vaccination and that these mice remained disease free beyond 250 days after injection of the P210Bcr-Abl positive 32D leukemia cells, whereas C56BL/6J test mice treated with TBI and TCDBMT without DLI from vaccinated donors nor sc BcrAbl/ecdCD40L sc booster vaccination following injection with the p210Bcr-Abl positive 32D myeloid leukemia cell line all died by day 32. Mice treated with TBI, TCDBMT, DLI from unvaccinated donors followed by vaccination of the recipient with 3 sc BcrAbl/ecdCD40L protein injections exhibited a degree of leukemia suppression that was equal to mice receiving TBI, TCDBMT, DLI from a BcrAbl/ecdCD40L VPP vaccinated donor and BcrAbl/ecdCD40L vaccination. To test the effect of the TAA/ecdCD40L VPP vaccine against an antigen associated with an epithelial neoplasm, we injected 100,000 E7 positive TC-1 mouse cancer cells into syngeneic C57BL6J mice followed in 3–5 days by myeloablative doses of TBI and engrafting doses of TCDBMT. Three days later, the mice received 10 million spleen cells from syngeneic donor mice previously vaccinated with the E7/ecdCD40L VPP vaccine. Finally, 4 weeks later, the test mice received sc E7/ecdCD40L protein booster injections. The vaccinated mice achieved much greater degrees of tumor suppression than was seen following TBI and TCDBMT without DLI from vaccinated donors. These studies show that it is possible to induce a robust adaptive immune response by vaccination with the TAA/ecdCD40L VPP vaccine even in severely lymphopenic individuals.
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