Selective Expansion of Viral Variants following Experimental Transmission of a Reconstituted Feline Immunodeficiency Virus Quasispecies

Following long-term infection with virus derived from the pathogenic GL8 molecular clone of feline immunodeficiency virus (FIV), a range of viral variants emerged with distinct modes of interaction with the viral receptors CD134 and CXCR4, and sensitivities to neutralizing antibodies. In order to assess whether this viral diversity would be maintained following subsequent transmission, a synthetic quasispecies was reconstituted comprising molecular clones bearing envs from six viral variants and its replicative capacity compared in vivo with a clonal preparation of the parent virus. Infection with either clonal (Group 1) or diverse (Group 2) challenge viruses, resulted in a reduction in CD4+ lymphocytes and an increase in CD8+ lymphocytes. Proviral loads were similar in both study groups, peaking by 10 weeks post-infection, a higher plateau (set-point) being achieved and maintained in study Group 1. Marked differences in the ability of individual viral variants to replicate were noted in Group 2; those most similar to GL8 achieved higher viral loads while variants such as the chimaeras bearing the B14 and B28 Envs grew less well. The defective replication of these variants was not due to suppression by the humoral immune response as virus neutralising antibodies were not elicited within the study period. Similarly, although potent cellular immune responses were detected against determinants in Env, no qualitative differences were revealed between animals infected with either the clonal or the diverse inocula. However, in vitro studies indicated that the reduced replicative capacity of variants B14 and B28 in vivo was associated with altered interactions between the viruses and the viral receptor and co-receptor. The data suggest that viral variants with GL8-like characteristics have an early, replicative advantage and should provide the focus for future vaccine development.

以源自猫免疫缺陷病毒（FIV）致病性GL8分子克隆的病毒进行长期感染后，出现了一系列与病毒受体CD134、CXCR4相互作用模式各异，且对中和抗体敏感性不同的病毒变异株。为评估该病毒多样性在后续传播过程中是否得以维持，研究人员重构了一套合成准种，其由携带6种病毒变异株囊膜蛋白（env）基因的分子克隆组成，并在体内将其复制能力与亲本病毒的单克隆制剂进行对比。分别以单克隆（第1组）或多样性（第2组）攻毒病毒感染动物后，两组均出现CD4阳性淋巴细胞减少、CD8阳性淋巴细胞增多的现象。两组受试动物的前病毒载量水平相似，均于感染后10周达到峰值；但第1组动物可实现并维持更高的病毒载量平台设定点（set-point）。第2组中各病毒变异株的复制能力存在显著差异：与GL8亲缘关系最近的变异株病毒载量更高，而携带B14、B28囊膜蛋白的嵌合变异株复制效果较差。这些变异株的复制缺陷并非由体液免疫应答抑制所致，因为本研究周期内未检测到病毒中和抗体的产生。同样，尽管可检测到针对囊膜蛋白抗原表位的强效细胞免疫应答，但感染单克隆或多克隆接种物的受试动物之间未出现定性差异。不过体外实验表明，B14与B28变异株在体内复制能力降低的原因，与其与病毒受体及共受体的相互作用发生改变相关。本研究数据提示，具有GL8样特征的病毒变异株具有早期复制优势，应成为未来疫苗研发的重点方向。