explain with references why it has been so difficult to develop a

1.  Explain with references why it has been so difficult to develop a vaccine against human immunodeficiency virus (HIV) and (2) discuss one promising new immune approach and one promising non-immune approach for understanding and/or treating AIDS

Instructions

1. Write a paper consisting of at least 2 pages of text that answers these questions. Use 1 x 1 x1 x 1 inch margins all around, double space, with 12 point font and submit electronically only as a MicrosoftWord document. Do not count a figure as text.
2. When you find reference(s) to answer these questions, provide a PDF copy of the reference. 

All references must come only from the peer review literature as found in PubMed

write from a very scientific view, be sure to write specifically about the question, and give details. give a brief introduction about the virus and how does it work