Human B-cell malignancies display on their surface, membrane-associated immunoglobulin (Ig). The variable regions at the amino terminal ends of both heavy and light chains (VH and VL) of Ig contain clonal specific epitopes that represent tumor specific antigens. The cloning and sequencing of VH cDNAs from tumor specimens of patients with B-cell lymphomas allow us to generate different synthetic peptides based upon these sequences. This will be exploited to test vaccination strategies in which patients' dendritic cells are pulsed with these peptides and their ability to induce tumor specific immunity will be examined.
In Aim 1, peptides corresponding to hypervariable (CDR1-3) regions of B-cell lymphomas that have either germline or somatically mutated sequences are being tested.
In Aim 2 peptides corresponding to the more conserved germline and somatically mutated framework VH regions are being tested for immunogenicity. In these first two vaccination strategies (Aims l and 2) we will use synthetic peptides of 11-30 amino acids to pulse DC's which would be expected to take up (by macropinocytosis), process and present small peptides in the context of MHC Class 1 and ll to autologous lymphocytes.
In Aim 3, smaller synthetic peptides (9-mers) which are expected to bind directly to Class I on dendritic cells without processing, are selected from the entire tumor-associated VH region based upon optimal MHC Class I binding strengths that are predicted by peptide binding motifs specific for an HLA allele expressed by the patient.
In Aim 4, patients' dendritic cells are transfected with mammalian expression vectors encoding either selected VH region peptides or the entire tumor associated VH region and the transfected dendritic cells tested for immunogenicity. In all 4 Aims, the vaccination strategies are evaluated for their ability to induce protective anti-tumor immunity using a human/SCID mouse chimeric model in which patients' peptide-pulsed or transfected dendritic cells, along with patients' lymphocytes, are engrafted in SCID mice and subsequently challenged with autologous tumor cells. Peptide pulsed or transfected D.C. are also evaluated in vitro for their ability to provoke tumor specific cytotoxic T lymphocytes. These results are expected to define immunogenic VH region peptides and to establish an optimal clinical strategy for the vaccination of patients with B cell malignancies. Valuable insights are also anticipated with respect to designing vaccination protocols for other tumors where a tumor specific antigen has been identified.
