Lymphocyte-activation gene 3

Lymphocyte-activation gene 3, also known as LAG-3, is a

LAG-3 is closely related to CD4,^[9] with which it shares the ability to bind MHC class II molecules.^[10] Although there has been conflicting information on which motifs in the LAG-3 cytoplasmic tail are important for function,^[11][12][13] evolutionary conversation patterns^[14][15] combined with functional studies^[12][13] imply that the evolutionarily conserved core function of LAG-3 is an inhibitory competition through an immunoreceptor tyrosine-based inhibitory motif (ITIM)–like motif with the activating receptors CD4 or CD8 for binding the kinase LCK.^[14]

Gene

The LAG3 gene contains 8 exons. The sequence data, exon/intron organization, and chromosomal localization all indicate a close relationship of LAG3 to CD4.^[5] The gene for LAG-3 lies adjacent to the gene for CD4 on human chromosome 12 (12p13) and is approximately 20% identical to the CD4 gene, ^[16] and this gene organization can already be found in sharks.

Protein

The LAG3 protein, which belongs to

Fibrinogen-like protein1 FGL1, a liver-secreted protein, is another (major) LAG3 functional ligand independent of MHC-II.^[25]

LAG3 also helps maintain CD8⁺ T cells in a tolerogenic state^[16] and, working with PD-1, helps maintain CD8 exhaustion during chronic viral infection.^[26]

LAG3 is known to be involved in the maturation and activation of dendritic cells.^[27]

Use as a pharmaceutical and as a drug target

There are three approaches involving LAG3 that are in clinical development.

• The first is
  IMP321,^[28] a soluble LAG3 which activates dendritic cells.^[29]
• The second are antibodies to LAG3 which take the brakes off the anti-cancer immune response.
  PD-1 since antibodies to these two checkpoints only activate effector T cells, and do not inhibit Treg activity, whereas an antagonist LAG-3 antibody can both activate T effector cells (by downregulating the LAG-3 inhibiting signal into pre-activated LAG-3+ cells) and inhibit induced (i.e. antigen-specific) Treg suppressive activity.^[32] Combination therapies are also ongoing involving LAG-3 antibodies and CTLA-4 or PD-1 antibodies.^[8][30]
• The third are agonist antibodies to LAG3 in order to blunt an autoimmune response. An example of this approach is
  plaque psoriasis).^[33]

In May 1996 scientists at the University of Florence showed that CD4⁺ T cells that were LAG-3⁺ preferentially expressed IFN-γ, and this was up-regulated by IL-12^[39] while in 1997 the same group showed that IFN-γ production was a driver of LAG-3 expression during the lineage commitment of human naive T cells.^[40] Subsequent work at the Sapienza University of Rome in 1998 showed that IFN-γ is not required for expression but rather for the up-regulation of LAG-3.^[41] The Triebel group in 1998 established that LAG-3 expression on activated human T cells is upregulated by IL-2, IL-7 and IL-12 and also showed that expression of LAG-3 may be controlled by some CD4 regulatory elements.^[42] In 1998 the Triebel group showed that, on T cells, LAG-3 down-modulates their proliferation and activation when LAG-3/MHC Class II co-caps with CD3/TCR complex.^[43] This relationship was confirmed in 1999 with co-capping experiments and with conventional fluorescence microscopy.^[44] In 1999 Triebel showed that LAG-3 could be used as a cancer vaccine, through cancer cell lines transfected with LAG-3.^[45]

2000 to 2009.

In 2001 the Triebel group identified a LAG3-associated protein, called LAP, that seemed to participate in immune system down-regulation.^[46] Also in 2001 the Triebel group reported finding LAG3 expression on CD8⁺ tumor-infiltrating lymphocytes, with this LAG3 contributing to APC activation.^[47] In August 2002 the first phenotypic analysis of the murine LAG-3 was reported by a team at St. Jude Children's Research Hospital in Memphis.^[48] Molecular analysis reported by the St. Jude Children's Research Hospital team in November 2002 demonstrated that the inhibitory function of LAG-3 is performed via the protein's cytoplasmic domain.^[11] In 2003 the Triebel group was able to identify the MHC class II signal transduction pathways in human dendritic cells induced by LAG3.^[49] while the St. Jude Children's Research Hospital team showed that the absence of LAG3 caused no defect in T cell function.^[22]

In May 2004 the St. Jude Children's Research Hospital team showed, through LAG3 knockout mice, that LAG-3 negatively regulates T cell expansion and controls the size of the memory T cell pool.^[23] This was in spite of earlier in vitro work that seemed to suggest that LAG-3 was necessary for T cell expansion.^[22] Work at Johns Hopkins University published in October 2004 identified LAG3's key role in regulatory T cells.^[24] The St. Jude Children's Research Hospital team reported in December 2004 that LAG-3 is cleaved within the D4 transmembrane domain into two fragments that remain membrane-associated: a 54-kDa fragment that contains all the extracellular domains and oligomerizes with full-length LAG-3 (70 kDa) on the cell surface via the D1 domain, and a 16-kDa peptide that contains the transmembrane and cytoplasmic domains and is subsequently released as soluble LAG-3.^[50]

In January 2005 scientists at the D'Annunzio University of Chieti–Pescara showed that LAG-3 expression by tumour cells would recruit APCs into the tumour which would have Th1 commitment.^[51] Scientists working with AstraZeneca reported in March 2005 that SNPs on LAG3 conferred susceptibility to multiple sclerosis^[52] although later work at the Karolinska Institute showed no significant association.^[53] In June 2005 the Triebel group showed that antibodies to LAG-3 would result in T cell expansion, through increased rounds of cell division which LAG-3 signalling would otherwise block.^[54] In July 2005 scientists at the Institute for Research in Biomedicine in Bellinzona established that LAG3 expression on B cells is induced by T cells^[19]

In 2006 scientists at the

In 2009 the St. Jude Children's Research Hospital group reported that LAG3 appeared on plasmacytoid dendritic cells.[20] Scientists at the University of Tokyo showed that LAG-3 was a marker of Tregs that secrete IL-10.^[59]

2010 to 2015.

In 2010 scientists at

In 2011 scientists studying transplantation biology at Massachusetts General Hospital reported that when antibodies to CD40L induced tolerance in allogeneic bone marrow transplantation, LAG3 was part of the mechanism of action in CD8+ cells.^[65] Scientists at INSERM, working with the Triebel group, showed that the binding of MHC class II molecules on melanoma cells to LAG3 would increase resistance to apoptosis, providing evidence that antibodies to LAG3 would be relevant in melanoma.^[66] The St. Jude Children's Research Hospital group showed that LAG3 can play a modulating role in autoimmune diabetes.^[67] Microbiologists at the University of Iowa demonstrated that blockade of PD-L1 and LAG-3 was a valid therapeutic strategy for Plasmodium infection.^[68]

In 2012 the St. Jude Children's Research Hospital group showed that LAG-3 and PD-1 synergistically regulate T-cell function in such a way as to allow an anti-tumoral immune response to be blunted.^[69] Scientists at Hanyang University in Seoul showed that tetravalent CTLA4-Ig and tetravalent LAG3-Ig could synergistically prevent acute graft-versus-host disease in animal models.^[70] In 2013 scientists at the San Raffaele Scientific Institute in Milan showed that LAG3 was a marker of type 1 Tregs.^[71]

In 2014 scientists at