The immunoglobulin heavy chain variable region is encoded as three separate libraries of elements in germ‐line DNA: VH, D and JH. To examine the order and regulation of their joining, we have developed assays that distinguish their various combinations and have used the assays to study tumor cell analogs of B‐lymphoid cells as well as normal B‐lymphoid cells. Abelson murine leukemia virus (A‐MuLV) transformed fetal liver cells ‐ the most primitive B‐lymphoid cell analog available for analysis ‐ generally had DJH rearrangements at both JH loci. These lines continued DNA rearrangement in culture, in most cases by joining a VH gene segment to an existing DJH complex with the concomitant deletion of intervening DNA sequences. None of these lines or their progeny showed evidence of VHD or DD rearrangements. Heavy chain‐producing tumor lines, representing more mature stages of the B‐cell pathway, and normal B‐lymphocytes had either two VHDJH rearrangements or a VHDJH plus a DJH rearrangement at their two heavy chain loci; they also showed no evidence of VHD or DD rearrangements. These results support an ordered mechanism of variable gene assembly during B‐cell differentiation in which D‐to‐JH rearrangements generally occur first and on both chromosomes followed by VH‐to‐DJH rearrangements, with both types of joining processes occurring by intrachromosomal deletion. The high percentage of JH alleles remaining in the DJH configuration in heavy chain‐producing lines and, especially, in normal B‐lymphocytes supports a regulated mechanism of heavy chain allelic exclusion in which a VHDJH rearrangement, if productive, prevents an additional VH‐to‐DJH rearrangement.

Highlights High prevalence of serological cross-reactivity against SARS-CoV-2 in pre-COVID-19 pandemic plasma samples from sub-Sahara Africa. Pre-COVID-19 pandemic plasma displayed strong reactivity against other human coronaviruses. Exposure to other coronaviruses may induce cross-reactive antibodies against SARS-CoV-2 in sub-Sahara Africa.

Human immunodeficiency virus type 1 (HIV-1) clade C causes >50% of all HIV infections worldwide, and an estimated 90% of all transmissions occur mucosally with R5 strains. A pathogenic R5 simian-human immunodeficiency virus (SHIV) encoding HIV clade C env is highly desirable to evaluate candidate AIDS vaccines in nonhuman primates. To this end, we generated SHIV-1157i, a molecular clone from a Zambian infant isolate that carries HIV clade C env. SHIV-1157i was adapted by serial passage in five monkeys, three of which developed peripheral CD4 ؉ T-cell depletion. After the first inoculated monkey developed AIDS at week 137 postinoculation, transfer of its infected blood to a naïve animal induced memory T-cell depletion and thrombocytopenia within 3 months in the recipient. In parallel, genomic DNA from the blood donor was amplified to generate the late proviral clone SHIV-1157ipd3. To increase the replicative capacity of SHIV1157ipd3, an extra NF-B binding site was engineered into its 3 long terminal repeat, giving rise to SHIV1157ipd3N4. This virus was exclusively R5 tropic and replicated more potently in rhesus peripheral blood mononuclear cells than SHIV-1157ipd3 in the presence of tumor necrosis factor alpha. Rhesus macaques of Indian and Chinese origin were next inoculated intrarectally with SHIV-1157ipd3N4; this virus replicated vigorously in both sets of monkeys. We conclude that SHIV-1157ipd3N4 is a highly replication-competent, mucosally transmissible R5 SHIV that represents a valuable tool to test candidate AIDS vaccines targeting HIV-1 clade C Env.

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