So far four nectins have been identified in humans, namely nectin-1, nectin-2, nectin-3 and nectin-4. These four family members have also been found in most other well studied mammals. Also, five Necls have been identified, these are: Necl-1, Necl-2, Necl-3, Necl-4 and Necl-5.
All nectins and all Necls share the same overall structure defined by three extra cellular immunoglobulin domains, a single transmembrane helix and an intracellular domain. For all nectins the intracellular domain can bind a scaffold protein named afadin (the product of the MLLT4 gene).
All nectins and Necls can form homo-cis dimers, meaning a dimer of two alike molecules on the same cell membrane. Following the homo-dimer formation they can trans-interact in an either heterophilic or homophilic manner. The network of the nectin and Necl trans-interactions has been characterized. Recent structural reports reveal the physical and chemical determinants of homophilic interactions mediated by N-terminal IgV domains. In general, heterophilic interactions among nectins have higher affinity than their respective homophilic interactions.
Since the research of nectins has been approached from several angles there is still some controversy about the names of these proteins and the genes encoding them. The idea of grouping these proteins into nectins and Necls originates from Dr. Youhsimi Takais early studies of the proteins. Nectins and Necls are much related in function and protein structure and have been found to interact in a variety of way, which it is why it makes good sense to define them as families. However, if you consider the sequence of the genes encoding the proteins an alternative way of naming the proteins also make sense as pointed out by Thomas Biederer. Alternative names for nectins and Necls are listed below.
nectin-1 : PVRL1 (Poliovirus receptor-related 1), HveC (herpesvirus entry mediator C), CD111 (Cluster of Differentiation 111)
nectin-2 : PVRL2 (Poliovirus receptor-related 2), HveB (herpesvirus entry mediator B), CD112 (Cluster of Differentiation 112)
nectin-3 : PVRL3 (Poliovirus receptor-related 3), CD113 (Cluster of Differentiation 113)
necl-1 : CADM3 (Cell adhesion molecule 3), TSLL1 (TSLC1-like 1), SynCAM3 (Synaptic cell adhesion molecule 3), IGSF4B (Immunoglobulin super family member 4B)
necl-2 : CADM1 (Cell adhesion molecule 1), TSLC1 (Tumor suppressor in lung cancer 1), SynCAM1 (Synaptic cell adhesion molecule 1), IGSF4 (Immunoglobulin super family member 4), sgIGSF (Spermatogenic immunoglobulin superfamily), RA175
necl-3 : SynCAM2 (Synaptic cell adhesion molecule 2)
necl-4 : TSLL2 (TSLC1-like 2), SynCAM4 (Synaptic cell adhesion molecule 1)
necl-5 : Tage4, PVR (Poliovirus receptor), CD155
Enfortumab vedotin-ejfv was approved by the FDA in 2019; it is a Nectin-4-directed antibody drug conjugate that has shown clinical activity in metastatic urothelial cancer. 
Nectin-1 and nectin-3 have been shown to be involved in cellular adhesion in some neuronal synapses. Unlike many other cellular adhesion molecules they do not distribute evenly on axonal and dendritic side of the synapse. Instead, Nectin-1 is primarily found on the axonal side and nectin-3 primarily on the dendritic side. Nectin-1 serves as the entry receptor for Herpes Simplex Viruses 1 and 2, binding to the viral envelope glycoprotein gD, and for Pseudorabies Virus.
Recently, it has been found that nectin-4 can be found in the serum of patients suffering from lung cancer. This has led to speculations that this protein might be involved in some developing cancers and might even have a pharmaceutical potential.
Also, it has been well known for some time now, that necl-2 is down regulated in a variety of cancers. This is why necl-2 is also known as Tumor suppressor in lung cancer 1 (TSLC1).
- nectins at the US National Library of Medicine Medical Subject Headings (MeSH)
- Takai Y, Irie K, Shimizu K, Sakisaka T, Ikeda W (Aug 2003). "Nectins and nectin-like molecules: roles in cell adhesion, migration, and polarization". Cancer Science. 94 (8): 655–67. doi:10.1111/j.1349-7006.2003.tb01499.x. PMID 12901789.
- Fuchs, Anja; Colonna, M (October 2006). "The role of NK cell recognition of nectin and nectin-like proteins in tumor immunosurveillance". Seminars in Cancer Biology. 16 (5): 359–366. doi:10.1016/j.semcancer.2006.07.002. PMID 16904340.
- Miyoshi J, Takai Y (Sep 2007). "Nectin and nectin-like molecules: biology and pathology". American Journal of Nephrology. 27 (6): 590–604. doi:10.1159/000108103. PMID 17823505.
- https://www.fda.gov/drugs/resources-information-approved-drugs/fda-grants-accelerated-approval-enfortumab-vedotin-ejfv-metastatic-urothelial-cancer. Missing or empty
- "NECTIN1 nectin cell adhesion molecule 1 [Homo sapiens (human)] - Gene - NCBI".