Viral factors
• Extensive viral clade and sequence diversity
• Early establishment of latent viral reservoirs
• Viral evasion of humoral and cellular immune responses
• Immune correlates of protection unclear
• Antibody responses typically type-specific

Research limitations
• No method yet exists to elicit broadly reactive NAbs
• Limited interest from the pharmaceutical industry
•Funding Challenges
Table 1: Challenges in the Development of a preventive HIV-1 Vaccine.
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