**1. Introduction**

Extracellular vesicles are membrane vesicles. The extracellular vesicles are secreted by most cell types of any living organism from archaea, bacteria, and eukarya. Extracellular vesicles are isolated from biological fluids such as blood, semen, cerebrospinal fluid, and saliva [1, 2]. Exosomes are formed by the fusion of multivesicular bodies (MVBs) with the cell membrane and then released into the extracellular space [3]. Exosomes are extracellular vesicles with a diameter of 30–100 nm. Exosomes are used in therapeutic applications like a delivery system. The exosomes and retroviral vectors are efficient transporters of biotransformation. The exosomes are used in immunotherapies and biotherapies. Exosomes and lentiviruses are excellent vehicles to carry encapsulated cargo with reduced immunogenicity with multiple cell types and tissue barriers, including the blood-brain barrier. The inherent properties of exosomes are to enclose nucleic acids, proteins, lipids, and chemical agents. Exosomes have been considered to carry the coding, and non-coding RNA (miRNA and siRNA) along with the lentiviral vectors which give a stable integration into target cells [4–9]. Some findings proposed that the human immune deficiency virus (HIV) particles like exosomes contribute to HIV pathogenesis, but the recent findings reported that

#### **Figure 1.**

*A: View of an Multivesicular endosome (MVE) sparsely labelled with AuTf after a 20 min incubation at 37°C. note the apparent fusion of the MVE and the plasma membrane. This may represent incipient MVE exocytosis. Bar, 100 nm. × 107,000. Fig. B: View of MVE exocytosis in an unfixed reticulocyte. This cell was incubated for 30 min with AuTf, subjected to a 20 min chase with unconjugated transferrin, and then quick-frozen without prior fixation and freeze-substituted. Bar, 200 rim. × 61,000. Fig C: Freeze-fracture, deep-etch view of a large MVE filled with numerous inclusions. The remaining free lumen possesses a markedly lower protein concentration than the surrounding cytoplasm and is deeply etched. Bar, 200 nm. × 63,000. Fig. D: View of an MVE lightly labelled by AuTf after a 20 min incubation at 37°C. AuTf (white dots) is bound to the walls of the MVE and is clustered heavily around the inclusions, making the outline of the individual gold beads difficult to discern. Bar, 100 nm. × 127,000. All A, B, C, D figures are adopted from Harding et al. [11], figure source has permitted from the author).*

the exosomes exert an effect on the replication of HIV [10]. The potential research on exosomes will be helpful in the vaccine or therapeutic design to treat HIV patients along with antiretroviral therapy. The exosome adopted picture is given in **Figure 1**.
