The human APOBEC superfamily consists of eleven cytidine deaminase enzymes. Among them, APOBEC3 enzymes play a dual role in antiviral immunity and cancer development. APOBEC3 enzymes, including APOBEC3A (A3A) and APOBEC3B (A3B), induce mutations in viral DNA, effectively inhibiting viral replication but also promoting somatic mutations in the host genome, contributing to cancer development. A3A and A3B are linked to mutational signatures in over 50% of human cancers, with A3A being a potent mutagen. A3B, one of the first APOBEC3 enzymes linked to carcinogenesis, plays a significant role in HPV-associated cancers by driving somatic mutagenesis and tumor progression. The A3A_B deletion polymorphism results in a hybrid A3A_B gene, leading to increased A3A expression and enhanced mutagenic potential. Such polymorphism has been linked to an elevated risk of certain cancers, particularly in populations where it is more prevalent. This review explores the molecular mechanisms of APOBEC3 proteins, highlighting their dual roles in antiviral defense and tumorigenesis. We also discuss the clinical implications of genetic variants, such as the A3A_B polymorphism, mainly in HPV infection and associated cancers, providing a comprehensive understanding of their contributions to both viral restriction and cancer development.

High-risk Human Papillomavirus (HPV) infection is the main etiological factor for cervical carcinogenesis, although genetic cofactors also play a role. Single-nucleotide variants (SNVs) in the CTLA4 gene can alter the gene expression and immune response against HPV, influencing cervical malignancy progression. This study analyzed the association of the alleles, genotypes, and haplotypes of the CTLA4 SNVs rs5742909 (−318 C>T), rs231775 (+49 A>G), and rs3087243 (+6230 G>A) with HPV infection, the development of low-grade squamous intraepithelial lesions (LSILs), high-grade squamous intraepithelial lesions (HSILs), and cervical cancer in 445 women treated by the public health service of Paraná, Brazil. Peripheral blood and cervical secretion samples were collected for genomic DNA extraction, CTLA4 SNV genotyping, and HPV detection via PCR. Statistical analyses used p < 0.05. The HPV-negative control group included 181 women, while the HPV-positive group included 264 women. The HPV-positive group was divided into no lesion (n = 84), LSILs (n = 19), HSILs (n = 56), and cervical cancer (n = 105). The T allele of −318 C>T and the TAG haplotype were associated with increased susceptibility to HPV infection, HSILs, and cervical cancer. These findings suggest that the T allele of −318 C>T and the TAG haplotype may serve as potential molecular biomarkers for HPV susceptibility and worse prognosis.