MHC-I-restricted CTL responses of H-2d (Ld+ or Ld−) and F1 H-2dxb mice to hepatitis B surface Ag (HBsAg) are primed by either DNA vaccines or HBsAg particles. The Dd/S201–209 and Kd/S199–208 epitopes are generated by processing endogenous HBsAg; the Kb/S208–215 epitope is generated by processing exogenous HBsAg; and the Ld/S28–39 epitope is generated by exogenous as well as endogenous processing of HBsAg. DNA vaccination primed high numbers of CTL specific for the Ld/S28–39 HBsAg epitope, low numbers of CTL specific for the Dd/S201–209 or Kd/S199–208 HBsAg epitopes in BALB/c mice, and high numbers of Dd/S201–209- and Kd/S199–208-specific CTL in congenic H-2d/Ld− dm2 mice. In F1dxb mice, the Kd-, Dd-, and Kb-restricted CTL responses to HBsAg were strikingly suppressed in the presence but efficiently elicited in the absence of Ld/S28–39-specific CTL. Once primed, the Kd- and Dd-restricted CTL responses to HBsAg were resistant to suppression by immunodominant Ld/S28–39-specific CTL. The Ld-restricted immunodominant CTL reactivity to HBsAg can thus suppress priming to multiple alternative epitopes of HBsAg, independent of the processing pathway that generates the epitope, of the background of the mouse strain used, and of the presence/absence of different allelic variants of the K and D MHC class I molecules.

The immunodominant, conformational “a” determinant of hepatitis B surface Ag (HBsAg) elicits Ab responses. We selectively expressed the Ab-binding, glycosylated, native a determinant (residue 120–147) of HBsAg in a fusion protein containing C-terminally the HBsAg fragment SII (residue 80–180) fused to a SV40 T-Ag-derived hsp73-binding 77 aa (T77) or non-hsp-binding 60 aa (T60) N terminus. A DNA vaccine encoding non-hsp-binding secreted T60-SII fusion protein-stimulated murine Ab responses with a similar efficacy as a DNA vaccine encoding the secreted, native, small HBsAg. A DNA vaccine encoding hsp73-binding, intracellular T77-SII fusion protein-stimulated murine Ab responses less efficiently but comparable to a DNA vaccine encoding the intracellular, native, large HBsAg. HBsAg-specific Abs elicited by either the T60-SII-expressing or the T77-SII-expressing DNA vaccine suppressed HBsAg antigenemia in transgenic mice that produce HBsAg from a transgene in the liver; hence, a biologically active B cell response cross-reacting with the native, viral envelope epitope was primed by both DNA vaccine constructs. HBsAg-specific Ab and CTL responses were coprimed when an S20–50 fragment (containing the immunodominant, Ld-binding epitope S28–39) of HBsAg was fused C-terminally to the pCI/T77-SII sequence (pCI/T77-SII-Ld DNA vaccine). Chimeric, polyepitope DNA vaccines encoding conformational, Ab-binding epitopes and MHC class I-binding epitopes can thus efficiently deliver antigenic information to different compartments of the immune system in an immunogenic way.

The incorporation of linear and conformational antibody-binding epitopes into polyepitope, chimeric antigens with satisfactory immunogenicity is a challenge. We selectively expressed antigen fragments encoding the linear e2 epitope (C_79–149) of hepatitis B virus (pre)core antigen (HBc/eAg) and the conformational ‘a’ epitope (S_80–180) of hepatitis B surface antigen (HBsAg) in a novel system. The domains were expressed as chimeric antigens containing either heat shock protein (hsp)73-binding simian virus 40 large tumor antigen (e.g. T₇₇) or non-hsp-binding (e.g. T₆₀) sequences at their N-termini. We compared their type of expression with their immunogenicity for B cells (when delivered as a DNA vaccine). The type of expression investigated included their level of expression, the secretion or intracellular expression of the antigen and the stress protein (hsp)-associated versus nonassociated expression. The linear e2 epitope of HBc/eAg was efficiently expressed as an intracellular, hsp73-binding fusion protein, and efficiently primed an HBc/eAg-specific antibody response when delivered in this form. The conformational ‘a’ epitope of HBsAg most efficiently stimulated B cells as a secreted, non-hsp-associated fusion protein. These data demonstrate that different B cell-stimulating epitopes of vaccine-relevant viral antigens can be selectively isolated and expressed in suitable expression systems, but that the requirements that have to be fulfilled to obtain optimal immunogenicity differ strikingly between individual epitopes.

In an earlier communication (Aboul-Dahab et al. 1958) the authors reported on the variability of response to chloromycetin of infants admitted to hospital (August 1954-1955) during a major study on gastroenteritis (Tawil et al., 1959). A relevant feature was the high incidence of relapses among the inpatients of period 3 (May 28, 1955, to August 15, 1955) of that study, particularly the chloromycetin-treated group of cases. The relapses usually coincided with the recovery, from the stools, of strains of Escherichia coli that were resistant to chloromycetin. These strains possessed the same somatic 0 antigen and Dr. F. Qrskov, who kindly checked our findings,

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