Response to Letter to the Editor

We agree with Dr. Alexander’s suggestion that theintegrity of synthetic peptides needs to be carefullyascertained for in vitro immunization studies. Thesynthetic peptide used in our recently published study[1] was confirmed to be a 9-mer peptide by mass spec-troscopy performed by the manufacturer (ResearchGenetics, Birmingham, AL). The same peptide corre-sponding to residues 146–154 of prostate specific an-tigen (PSA146–154) has been synthesized on four sub-sequent occasions over a two year period. Each prepa-ration has been confirmed by mass spectroscopy andhas mediated specific lysis by the original (CTL) line.We are examining whether the PSA 146–154 peptide isnaturally processed and presented for CTL recogni-tion by tumor cells that endogenously synthesize PSAprotein. It is interesting to note that Correale et. al.recently reported that an HLA-A2-restricted CTL lineelicited with an overlapping peptide corresponding toresidues 141–150 of PSA specifically lyses cells of theHLA-A2 phenotype that endogenously produce PSA

protein [2]. The PSA 141–150 peptide shares the po-tential to form disulfide bridges via the side chain ofthe cystine residue at position 149, yet appears to emu-late a naturally processed epitope from PSA protein.

David J. Peace, MDLoyola University Medical CenterCardinal Bernardin Cancer Center

Division of Hematology/Oncology2160 South First Avenue

Maywood, IL 60153

REFERENCES

1. Xue BH, Zhang Y, Sosman JA, Peace DJ: Induction of humancytotoxic T lymphocytes specific for prostate-specific antgen.Prostate 1997; 30:73–78.

2. Correale P, Walmsley K, Nieroda C, Zaremba S, Zhu M, SchlomJ, Tsang KY: In vitro generation of human cytotoxic T lympho-cytes specific for peptides derived from prostate-specific anti-gen. J Natl Cancer Institute 1997; 89:293–300.

The Prostate 32:74 (1997)

© 1997 Wiley-Liss, Inc.