MONOPALMITIC ACID-PEPTIDE CONJUGATES INDUCE CYTOTOXIC T-CELL RESPONSES AGAINST MALARIAL EPITOPES - IMPORTANCE OF SPACER AMINO-ACIDS

Cytolytic T cells (CTL) play a critical role in providing protection a gainst the liver stage of malaria infection. Previous investigations h ave shown that induction of CTL against peptide or proteins can be ach ieved by attachment of lipids. In the present study, we used the Plasm odium berghei circumsporozoite protein CTL epitope (SYIPSAEKT (PL76)). This peptide with cysteine-serine (CS) as spacer amino acids was coup led to palmitic acid (PA). The same CTL epitope containing only an ext ra serine was linked to mitoyloxy)-(2-RS)-propyl]-N-palmitoyl-(R)-cyst eine (tripam-C). Inbred mice [(BALB/c x C57BL/6)F1] were immunized int ravenously with the lipopeptides. Both types of lipopeptides induced s ignificant CTL responses after one injection. Immunization of the mono palmitic acid-peptide conjugate intraperitoneally emulsified in Freund 's complete adjuvant also induced a significant CTL response, but the magnitude was lower as compared to the intravenous route. The major ad vantages of the use of the simple monopalmitic acid-peptide conjugates are: (i) low costs of the fatty acid; (ii) coupling of lipid to pepti de can be performed using the peptide synthesizer during standard pept ide synthesis, and (iii) standard peptide methodology can be used for purification. To investigate whether a spacer amino acid sequence betw een the actual CTL epitope and PA is required for induction of an opti mal CTL response, we prepared monopalmitic acid-peptide conjugates wit h different spacer amino acids. A lipopeptide without a spacer amino a cid and another one containing the CS spacer sequence both induced a C TL response, whereas a lipopeptide with a serine as spacer failed to i nduce CTL. These results indicate that the amino acid spacer sequences influence the immunological properties of the palmitic acid-peptide c onjugates.