Topics: HIV Sero-discordant Couples, Transmission of HIV, lmmune System, CD4 cells, B-cells, T-cells, HIV Lifecycle, Replication errors, HIV-Induced Disease, MTCT, Mother-to-Child Transmission, Specific PMTCT Interventions, Antiretroviral Treatment, ARVs, NRTIs, ARV Drug Toxicity, Prophylaxis, ARV Prophylaxis, Post-sexual exposure prophylaxis, Post-Exposure Prophylaxis