Hybrid Tumor Vaccines David L. Liu, MD, PhD Professor of Surgery and Oncology Tumor Immunotherapy Division RedSun Institute 242 Dorchester Street, Boston, MA02127, USA

Tumor is a gene-mutated or molecule-mutated disease. Therefore, tumor cells should have expressed one or multiple types of tumor- specific antigens. Unfortunately, the immune system of the body does not recognize tumor-specific antigens because their weak immunogenicity, which leads to escape of tumor cells from immune surveillance.

Whole cell tumor vaccines or hybrid tumor vaccines have been studied in our laboratories since 1995.

Our innovative idea is that failed recognition of tumor-specific antigens by the immune system of the body is an issue of insufficient expression and presentation of tumor-specific antigens to the immune system rather than the consequence of inadequate immunity in tumor-bearing hosts.

Studies have confirmed that either a youth recipient or elderly one who receives an allogeneic graft is capable of rejecting a transplanted liver, lung or kidney. This fact strongly suggests that an individual should have sufficient immunity to reject a tumor weighing 1,000 to 2,000 grams if a specific immune reaction against tumor-specific antigens can be evoked.

Another innovative idea is that we further hypothesized that tumor antigens are hypo-immunogenicity that is unable to elicit an efficient antitumor immune reaction. Therefore, we believe that upregulation of activities of immune component cells do not mean enhanced anti-tumor immunity in tumor-bearing hosts.

A convinced example is that de novo tumors occur in some of recipients who received allogeneic transplantation of the liver or kidney, but the immune system of the recipient only rejects the transplanted liver or kidney rather than de novo tumor. Undoubtedly, activities of immune component cells in these subjects are high during the period of rejection episode.

Studies have shown that hybrid tumor vaccines (HTV), generating by fusion of activated antigen-presenting cells (APCs) with tumor cells, are highly efficient treatment in various tumors.

HTV produced by fusion of activated autologous B cells with hepatoma cells cured liver tumors in rats; HTV generated by fusion of A20 cells with E4 tumor cells cured brain tumors in mice; HTV formed by fusion of activated dendritic cells with MC38 tumor cells cured adenocarcinoma of the colon in mice. Again, HTV developed by fusion of allogeneic monocyte-derived dendritic cells with renal carcinoma cells cured patients with metastatic renal cell carcinoma.

Take together, the common strategy of these successful HTV treatments is to use activated APCs as “amplifiers” of tumor-specific antigens, upregulating expression and presentation of tumor-specific antigens to the immune system of tumor-bearing hosts.

All of these facts strongly suggested that one of current investigative directions of active immune therapy and tumor vaccines should be focused on upregulation of expression and presentation of tumor-specific antigens rather than over-activation of immune component cells in tumor-bearing hosts.

Current Status of Tumor Vaccines 1. Classical tumor vaccine. Mixing extracts of tumor cells with Bacilli Calmette-Guerin (BCG) or other immune adjuvant. Experimental studies and clinical trials have shown that this type of tumor vaccines is ineffective.

2. Anti-idiotypic antibody tumor vaccines. Idiotypic determinants expressed by immunoglobulins on the surface of neoplastic cells target for the immune response. For example, some lymphoma cells and melanoma cells express idiotypic determinants that can be used to induce polyclonal immunity against all available determinants on the surface of tumor cells.

3. Recombinant DNA tumor vaccines. To some degree, these tumor vaccines are effective. The problem with this method is that viral vector systems for transfection of gene product into cancer cells are not tumor tissue specific, and exogenous gene product may not enter into all malignant cells in vivo, particularly in distally metastatic lesions. Another pitfall of this vaccine is that the anti-cancer immunity is indirect because the immune reaction induced by this type of tumor vaccines is not evoked by tumor-specific antigens.

4. Whole Cell Tumor Vaccines or Hybrid Tumor Vaccines. Fusion of autologous or allogeneic or xenogenetic APCs with tumor cells to generate autologous or allogeneic or xenogenetic hybrid cells. Living Hybrids Vaccines. Irradiated Hybrids Vaccines.

5. Tumor Vaccines Netting-Tumor Antigens. Heating shock protein- based tumor cell extracts could cure mouse lung cancer and patients with malignant tumors. Phase-II clinical trials showed 20% of treated patients had significant regression of tumors.

LIP Tumor Vaccines LIP tumor vaccine is Dr. David Liu’s personal invention. LIP is the abbreviation of three commonly used biologic reagents which are approved to be used in clinic by FDA. Pre- immunization of 3 times with one of them to tumor-bearing host and then intra-tumoral injection with LIP vaccines, that cured several types of mouse tumors in C57BL6 mice and human tumors in nude mice by non-specific and specific immune reactions.

Currently, one realistic and feasible strategy to cure certain types of cancer is the development and generation of potent APCs as “amplifier of tumor-specific antigens to produce effective individual- specific hybrid tumor vaccines.

Prostate Cancer Cell Lines: LNcap and Crew

Weight of Various Size Tumors (Melanoma, Fresh Weight) 5x5mm = 0.2g tumor in a 20g bw mouse = 0.5kg tumor in a 50kg bw adult 6x6mm = 0.3g tumor in a 20g bw mouse = 0.75kg tumor in a 50kg bw adult 6x7mm = 0.4g tumor in a 20g bw mouse = 1.0kg tumor in a 50kg bw adult 7x7mm = 0.5g tumor in a 20g bw mouse = 1.25kg tumor in a 50kg bw adult 9x12mm = 1.0g tumor in a 20g bw mouse = 2.5kg tumor in a 50kg bw adult