[MoOrA1054] Extensive cross-neutralization of an HIV-1 subtype C vaccine strain by HIV-1 subtype C sera from four countries in southern Africa: the HIVNET 028 study

14th International AIDS Conference

Barcelona, Spain — July 7-12, 2002

[TITLE:] Extensive cross-neutralization of an HIV-1 subtype C vaccine strain by HIV-1 subtype C sera from four countries in southern Africa: the HIVNET 028 study

[AUTHOR(S):] L. Morris, N. Taylor, C. Gray¹, L. Oceguera, H. Sheppard, C. Hanson², R. Bures, D. Montefiori³

Int Conf AIDS. 2002 Jul 7-12;14:Abstract No. MoOrA1054

BACKGROUND:Antibodies capable of blocking HIV-1 entry are an important component of immune control and a desirable response to immunization with candidate HIV-1 vaccines. In preparation for HIV-1 vaccine trials, sera from 4 countries in southern Africa afflicted by HIV-1 subtype C were used to determine the extent of intra-subtype C and inter-subtype neutralization activity.

METHODS: Samples were collected from 78 recently HIV-1 infected individuals residing in Malawi (n=16), Zimbabwe (n=13), Zambia (n=20) and South Africa (n=29). Follow-up samples were available from 65 of these individuals approximately nine months later. Serum samples were assayed using a PBMC-based neutralization assay against a prototype subtype C vaccine strain from South Africa, Du151 and against other primary isolates of subtypes A, B and C.

RESULTS: At the initial time point 33 of the 78 (42%) serum samples showed activity against Du151 virus. A higher proportion of sera from Zambia showed activity (11/20, 55%) compared to South Africa (12/29, 41%), Malawi (6/16, 38%) and Zimbabwe (4/13, 31%). Although the proportion of sera that had neutralization activity did not increase at the later time point (28/65, 43%), there was an increase in serum titers from all 4 countries (median ID80 range 1:18 - 1:56). Further analysis revealed that these sera were significantly more potent at neutralizing a second subtype C isolate compared to a subtype B virus, while very few sera were able to neutralize a subtype A virus. This suggests that viral subtypes can sometimes be differentiated on the basis of neutralization by sera from infected individuals. Furthermore, there was a possible clustering of neutralization determinants in Malawi as was observed recently for South African samples.

CONCLUSIONS: These data indicate that there is extensive cross-neutralization of a subtype C vaccine strain by antibodies from HIV-1 subtype C infected persons residing in different countries in southern Africa.

Presenting author: Lynn Morris

1AIDS Virus Research Unit, National Institute for Communicable Diseases, AIDS Virus Research Unit, National Institute for Communicable Diseases, Private Bag X4, Sandringham, Johannesburg, 2131, South Africa.

2Viral and Rickettsial Disease Laboratory, California Department of Health Services, Richmond, California, United States.

3Center for AIDS Research, Duke University Medical Center, Durham, North Carolina, United States.

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