Lutz Jacob

Inhibition of tumor growth by recombinant vaccinia virus expressing GA733/CO17-1A/EpCAM/KSA/KS1-4 antigen in mice.

The human colorectal carcinoma (CRC)-associated GA733 antigen (Ag), also named CO17-1A/EpCAM/KSA/KS1-4, has been a useful target in passive immunotherapy of CRC patients with monoclonal antibody (mAb) and in active immunotherapy with anti-idiotypic antibodies or with recombinant protein. These approaches have targeted single epitopes (monoclonal anti-GA733 antibodies and anti-idiotypic antibodies) or extracellular domain epitopes (recombinant protein), primarily by B cells. To determine whether a reagent that induces immunity to a larger number of both B- and T-cell epitopes might represent a superior vaccine, we analyzed the capacity of full-length GA733 Ag expressing multiple potentially immunogenic epitopes and encoded by recombinant vaccinia virus (VV GA733-2) to induce humoral, cellular, and/or protective immunity in mice. VV GA733-2 induced Ag-specific antibodies that reacted predominantly to unknown epitopes on the Ag and lysed Ag-positive CRC targets in conjunction with murine peritoneal macrophages as effector cells. Immunized mice developed Ag-specific, proliferative and delayed-type hypersensitive lymphocytes. VV GA733-2 inhibited growth of ras-transformed syngeneic tumor cells expressing the human GA733 Ag in mice. These results suggest the potential of VV GA733-2 as a candidate vaccine for patients with CRC, possibly in combination with recombinant GA733-2–expressing adenovirus, which has been shown to induce cytolytic antibodies and T cells as well as tumor protective effects in mice. The combined vaccine approach may be superior to the use of either vaccine alone in patients who are pre-immune to both viruses.

Limitations of the severe combined immunodeficiency (SCID) mouse model for study of human B-cell responses.

Mice lacking functional T and B lymphocytes offer an in vivo animal model for the study of human immune functions. We have attempted to optimize the reconstitution of severe combined immunodeficiency (SCID) mice with human peripheral blood lymphocytes (PBL) using radiation, anti‐asialo GM1 antibody or cyclophosphamide (Cy) treatment of the mice and in vitro stimulation of human PBL with interleukin (IL)‐2 prior to their transfer to the mice. Total human IgG and tetanus‐toxoid (TT)‐specific human IgG responses of the mice were used as parameters of successful reconstitution. Treatment of the mice with anti‐asialo GM1 antibody significantly enhanced total human IgG levels, but not TT‐specific antibody responses, whereas irradiation or Cy treatment of the mice had no effect on human antibody production. In vitro treatment of human PBL with IL‐2 prior to engraftment significantly decreased total human IgG responses of human PBL‐grafted SCID mice. The immune responses of individual mice within a group were highly variable, which constitutes a major disadvantage of this model.

Tetanus toxoid‐specific T cell responses in severe combined immunodeficiency (SCID) mice reconstituted with human peripheral blood lymphocytes

SCID mice reconstituted with human peripheral blood lymphocytes (PBL) have repeatedly been shown 10 produce antigen‐specific B ceil responses. We have derived tetanus toxoid (TT)‐specific human T cell lines from cells of the peritoneal cavity, spleen and lymph nodes of SCID mice reconstituted with human PBL and boosted with TT. Establishment of these cell lines was dependent on the time interval between reconstitution of the mice with human PBL and initiation of lymphocyte cultures in vitro. When lymphocytes were collected from the mice 8 weeks after reconstitution, human lymphocytes with TT‐specific proliferative activity in vitro were isolated from the peritoneal cavity and spleen, but long‐term cell lines could not be established after repeated lymphocyte stimulation with TT. IL‐2 and autologous Epstein Barr virus‐transformed B cells. In contrast, three long‐term (>10 months) TT‐specific human T cell lines were established from lymphocytes collected from two of the eight mice in the group 4 weeks after reconstitution. The T cell lines were either CD4+ (two lines derived from peritoneal cavity and lymph node, respectively) or CD8+ (one line derived from spleen) and all expressed CD3, T cell receptor α/β, and human histocompatibility leucocyte class I antigen. The T cell lines, however, lacked cytotoxic, helper and suppressor activities. Thus, SCID mice can support human T cells that actively migrate to various organs and respond to antigenic stimuli both in vivo and in vitro, but these T cells lack characteristic functions.

Recombinant CD63/ME491/Neuroglandular/NKI/C-3 Antigen Inhibits Growth of Established Tumors in Transgenic Mice

Attempts to vaccinate against tumors can be hindered by the induction of immunological tolerance to the target Ag as a result of Ag expression on normal tissues. In this study, we find that transgenic mice expressing the melanoma-associated Ag CD63/ME491/neuroglandular/NKI/C-3 on their normal tissues do, in fact, exhibit immunological tolerance to the Ag, recapitulating the conditions in cancer patients. In these mice, growth of murine melanoma cells expressing the Ag after gene transfer was inhibited by immunization with Ag-expressing recombinant vaccinia virus combined with IL-2, but not by immunization with the protein alone, anti-idiotypic Abs, or irradiated tumor cells. The effect of the recombinant virus was demonstrated both for nonestablished and established tumors. Infiltration with both CD4+ and CD8+ T lymphocytes was significantly more extensive in tumors from experimental mice than in tumors from control mice. MHC class I-positive, but not class I-negative, tumors were inhibited by the vaccine, suggesting that MHC class I-restricted T lymphocytes play a role in the antitumor effects. Abs did not appear to be involved in the vaccine effects. CD63 was immunogenic in 2 of 13 melanoma patients, pointing to the potential of this Ag, combined with IL-2, as a vaccine for melanoma patients.

Animal models of human-derived cancer vaccines.

Preclinical cancer vaccine studies must address vaccine safety, immunogenicity, and efficacy, as well as mechanism of vaccine action. Animal models of vaccines employing human tumor-associated antigen or epitopes (TAA, TAE) differ fundamentally from those employing tumor-specific antigens or epitopes (TSA, TSE). TSA and TSE vaccines will most likely demonstrate similar toxicity, immunogenicity, and efficacy in both tumor-bearing animals and patients. In contrast, TAA/TAE immunizations may have to overcome a host’s immunological tolerance to TAA/TAE expressed not only on tumor, but also on normal tissues; immunity to TAA/TAE will potentially target normal tissues and thus may induce autoimmunity. Various experimental models for human-derived TAA/TAE vaccines have been developed. These models include transgenic mice, mice with severe combined immunodeficiency (SCID), and non-human primates. Recently, unique animal models of TAA/TAE cancer vaccines have been developed, taking advantage of the discovery of animal tissue antigens with significant sequence homologies to human TAA/TAE. These models mimic perhaps most closely the situation in cancer patients.