**2. The exosomes association with HIV-1 patient**

The circulated exosomes in plasma are small and nanometre in size. Due to the small size, the exosomes are easily separated from human plasma through low density, differential ultracentrifugation, or ultrafiltration [12]. The exosomes are isolated from the semen for HIV-1 infection assays [13]. The exosomes in the host play an important role in HIV-1 infection, releasing intracellular and extracellular material and establishing cell-cell communication. The exosome study in HIV research is a hotspot because it has great significance in predicting acquired immunodeficiency syndrome (AIDS). The microparticles containing the chemokine receptor CCR5, the principal coreceptor for macrophage-tropic human immuno-deficiency virus-1 was released from the surface of the CCR5+ Chinese hamster ovary cells and peripheral blood mononuclear cells. It proves that intercellular communication is associated with the cellular membranes of the HIV-1 infection [14]. Exosomes utilise the primary and secondary host cells. The human T cell immunoglobin mucin (TIM) proteins are used by retroviruses, such as HIV, for viral entry. The TIM1 proteins promote the infection

#### *Exosomes and HIV-1 Association in AIDS-Defining Patients DOI: http://dx.doi.org/10.5772/intechopen.101919*

of multiple viruses, such as HIV, through virion-associated phosphatidylserine [15]. As AIDS is incurable by antiretroviral therapy, a hypothesis is explained that the 'Trojan exosomes' can be a novel approach to vaccine development [16].

HIV-1 patients in antiretroviral therapy may develop the risk of non-AIDS-defining-cancers (NDCs). The transactivation response RNA containing exosomes from the HIV-1 infected T cells promotes the growth and progression of particular NADCs. In the host, the HIV-infected T cell exosome enters through the epidermal growth factor receptor by stimulating ERK1/2 phosphorylation via the EGF/TLR3 dependent manner leading to NADCs [17]. HIV-1 infected patients are more likely aggressive to develop cervical cancer. The HIV-1-associated exosomes promote the growth and progression of cervical cancer in HIV-1 patients [18]. A study reported the presence of the transactivation response element (TAR) miRNA encoded by HIV-1 infected cells and patient sera. This TAR miRNA was isolated from the exosomes derived from the HIV-1 infected cells. From the study, it was observed that the HIV-1 RNA molecules within the exosome helped in the intercellular viral spread in infected host cells [19]. This TAR RNA stimulated the production of proinflammatory cytokines from exosomes derived from HIV-1 infected cells [20]. The stable epigenetic repression of the HIV-1 expression *in vivo* was observed by the exosome-mediated systematic delivery of therapeutic cargo [21]. An engineered exosome Tat protein was used as a new class of biologic product to activate the latently HIV-1 infected primary CD4+ lymphocytes [22]. A research study found that the *Mycobacterium tuberculosis* drug-resistant strains secreted from exosomes by macrophages reactivate HIV-1 induced through oxidative stress. Proteomic information on several host factors, such as galectins, HSP90, HIF-1α in the *Mtb* specific reactivation, promotes the HIV-1 reactivation in the host. This study of this redox and bioenergetics basis of HIV-1 TB coinfection would be an effective therapeutic strategy [23].

Exosomes are nano-sized membrane vesicles released by fusion of the multivesicular body or the organelle of the endocytic pathway origin with the plasma membrane of the cells. The exosome biogenesis is an endosomal sorting complex required for transport (ESCRT) dependent or ESCRT independent. The endosomal pathways are not entirely separated but the different subpopulations of exosomes work synergistically in different cell types of machinery. The cell type or cellular machinery is an important factor that controls the secretion of exosomes [24]. The formation of the exosome is behind with multiple mechanisms. In the early endosome formation, the best mechanism involves the recruitment of the endosomal sorting complex required for transport (ESCRT) machinery to the ubiquitinated proteins. The ESCRT complex is made up of four protein complexes (ESCRT-0, -I, -II, and -III) along with accessory proteins (Alix, VPS4, and VTA-1). These protein complexes bind to the exosome cargos through the intraluminal vesicles (ILVs). One of the ESCRT-III complexes induces the inward budding and fission of the vesicles to form the microvesicular bodies [25–28]. The exosome cargos formation depends on the synthesis of ceramide as a mechanism to induce the vesicle curvature and budding [29]. The exosome formation depends on the synthesis of the tetraspanin-mediated organisation of specific proteins, such as the amyloidogenic protein and pre-melanosome protein [30, 31]. After the formation of exosomes, the exosomes played an important role in cellular functions such as cellular migration and invasion, immunity, normal development and adult physiology, fertilisation and mating behaviour, nervous system [24]. Exosomes and HIV-1 particles share important features in biogenesis, biophysical, molecular, and cellular uptake mechanisms. Both HIV-1 and exosomes are surrounded by a phospholipid bilayer in a size of 100–200 nm but their separation is a technical challenge by

centrifugations. Exosomes are membrane-derived vesicles that harbour genomic, proteomic, and lipid cargos and also participate in the progression of HIV-1 pathogenesis. Exosomes derived from the HIV-1 infected dendritic cells were more infective than the cell-free HIV-1 or exosome-derived T cells. During HIV-1 infection, the exosomes


#### **Table 1.**

*Types of proteins and lipids in exosomes: The author has permitted the source [42].*

#### *Exosomes and HIV-1 Association in AIDS-Defining Patients DOI: http://dx.doi.org/10.5772/intechopen.101919*

from the dendritic cells contain fibronectin and galectin-3. In the T-cells exposed to exosomes cargo derived from HIV-1 infected dendritic cells, the gene expression of the pro-inflammatory cytokines IFN-γ, TNF-α, IL-1β, and RANTES and activation of p38/Stat pathways was observed [32]. A class of proteins called 'Tetraspanins' provides a powerful approach to distinguish exosomes and HIV-1 infected cells during the progression of the disease [33]. The Epstein–Barr virus (EBV) that causes tumours in humans induces the transfer of viral oncoprotein, LMP1, and a virus-encoded miRNA through exosome [34]. Exosomes are involved in viral transmission and immune sensing in the host. Hepatitis-A and hepatitis-C viruses use exosomes for viral transmission and antibody-mediated immune responses in the host [35]. The cytomegalovirus, the herpes simplex virus, human papillomavirus, the respiratory syncytial virus was mediated exosome cargo of various molecules, such as dendritic cell-specific ICAM-3 grabbing nonintegrin (DC-SIGN) and MHC-I and II [36].

The architecture of the exosome is very complex and contains proteins, nucleic acids, and lipids. Various databases are available for information on exosomal proteins, mRNA, MicroRNAs and lipids [37, 38]. The integrated database provides high-throughput datasets on vesicular components of prokaryotes, mammalian and nonmammalian eukaryotes extracellular vesicles [38]. An exosome contains several tetraspanins such as CD9, CD63, CD81, CD82 takes part in cell penetration, invasion and fusion events, heat shock proteins HSP70 and HSP90 involved in stress response in antigen binding and presentation, Alix, TSG101 proteins are involved in exosome release, annexins and Rab proteins are involved in membrane transport and fusion. The exosome biogenesis proteins Alix, flotillin, and TSG101 participate in exosome biogenesis. The proteins, such as TSG101, HSP70, CD81, and CD63, are highly enriched in exosomes and considered as the exosome marker proteins. Exosomes contain all types of RNA such as miRNA, ribosomal RNA, long non-coding RNA, piwi interacting RNA, transfer RNA, small nuclear and nucleolar RNA, etc. [39, 40]. Besides proteins and nucleic acids, the exosomes contain the lipids, such as phosphatidylserine, phosphatidic acid, arachidonic acid, cholesterol, and sphingomyelin. The human plasma and serum exosomes contain high-density lipoproteins (HDL), low/ very low-density lipoproteins (LDL/VLDL), Apo AI, Apo-B100, etc. [41]. The various proteins and lipid components of the exosome are given in **Table 1**.

Exosomes contain receptors for virus entry. SARS-CoV-2 spreaders are contributed by exosomes as they transfer the receptors CD9 and ACE2 to recipient cells susceptible to the SARS-CoV-2. During the SARS-CoV-2 infection, the SARS-CoV-2 virus is directed into the exosome pathways and the components are packaged into exosomes for secretion [43].
