A variety of host factors influence the ability of Human Immunodeficiency Virus (HIV)- type-1 to access and subsequently replicate within the cellular immune system. Understanding these factors is a crucial step in the development of novel therapeutic strategies including both chemotherapeutic treatments and vaccines. Although it has recently been reported that the CC chemokines RANTES, MIP-la and MIP-10 are the major HIV-1 suppressive factors derived from CD8+ T lymphocytes, this work demonstrates that these factors are not active at the level of transcriptional control and do not share identity with HIV-1 suppressive factors as measured in a transcriptional control assay. These other remaining factors are produced not only by CD8+ T lymphocytes, but by CD4+ T lymphocytes and cell lines derived from the other major leukocyte subsets. These factors are fractionable by standard chromatographic methodologies, and are active in models of both replication and transcription oflaboratory and primary HIV-1 isolates. This work should form the basis for several areas ofresearch related to modulation of HIV-1 replication and transcription. / Thesis / Master of Science (MSc)