Tuftsin

A naturally occurring tetrapeptide, Thr-Lys-Pro-Arg, cut from the Fc region of immunoglobulin G that stimulates macrophage and microglial phagocytosis through neuropilin-1, studied extensively in animal models of demyelination and infection yet never approved anywhere.

Also referenced as: Taftsin, TKPR, Tuftsin diacetate

Also appears in: Neuroprotection

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What is Tuftsin?

Tuftsin is a tetrapeptide, Thr-Lys-Pro-Arg, occupying residues 289 to 292 of the CH2 domain of the Fc region of the immunoglobulin G heavy chain, so it sits inside every IgG molecule and must be cut out enzymatically before it can act (Naim et al., Immunological Investigations, 1989;18(6):817-824; Yuan et al., Biochemistry and Biophysics Reports, 2023;34:101443). Victor Najjar and Kazuyuki Nishioka named and reported it in 1970 as a natural phagocytosis-stimulating peptide (Najjar and Nishioka, Nature, 1970;228(5272):672-673). Release from the parent immunoglobulin was attributed to a splenic endocarboxypeptidase, which is why loss of splenic function became the standard human setting for studying the peptide’s absence (Corazza et al., Lancet, 1991;337(8732):12-13). The free peptide has the molecular formula C21H40N8O6 and a molecular weight of about 500.6 g/mol, with CAS number 9063-57-4 (PubChem CID 156080).

Tuftsin is a genuine peptide of four natural L-amino acids rather than a peptidomimetic or a fusion construct. More than five decades after its discovery it has no approved product in any jurisdiction, no pending application and no registered human trial, and nearly all published work is preclinical. In current literature the sequence appears most often as a macrophage-targeting arm attached to liposomes, fusion proteins and nanocarriers rather than as a drug candidate. Selank, the Russian heptapeptide Thr-Lys-Pro-Arg-Pro-Gly-Pro, is the tuftsin sequence extended by a Pro-Gly-Pro tail.

How it works

• Neuropilin-1 is the receptor. Tuftsin and the higher-affinity analog TKPPR bind selectively to neuropilin-1 and block vascular endothelial growth factor binding to that receptor, and tetrameric TKPPR inhibits VEGF-induced autophosphorylation of VEGFR-2 on endothelial cells without directly blocking VEGF binding to VEGFR-2. Homology between TKPPR and the sequence encoded by exon 8 of VEGF led the authors to propose that at least some previously reported tuftsin effects are neuropilin-1 mediated (von Wronski et al., Journal of Biological Chemistry, 2006;281(9):5702-5710).
• Signaling runs through the TGF-beta pathway. Neuropilin-1 has an intracellular tail too short to signal alone and must work through coreceptors. In microglia, the inhibitor EG00229 prevents tuftsin binding and reverses the anti-inflammatory M2 shift it induces, blockade at TGF-beta receptor-1 disrupts the same shift, and tuftsin raises Smad3 phosphorylation while lowering Akt phosphorylation (Nissen et al., Journal of Neurochemistry, 2013;127(3):394-402).
• Phagocyte potentiation is the classical activity. The older literature credits tuftsin with potentiating phagocytosis, motility, immunogenic response and bactericidal and tumoricidal activity in macrophages and polymorphonuclear leukocytes, with binding sites isolated from rabbit peritoneal granulocytes and consistently low toxicity (Fridkin and Najjar, Critical Reviews in Biochemistry and Molecular Biology, 1989;24(1):1-40). Binding extends to monocytes and dendritic cells, the basis for using the sequence as a targeting ligand (Khan, Current Drug Targets, 2021;22(7):770-778).
• Peptidase susceptibility limits exposure. The free tetrapeptide is extremely vulnerable to enzymatic degradation in vivo, and that fragility is the stated reason its clinical development stalled. The stabilized derivative known as T peptide reached a half-life of 1.3 to 2.8 hours in beagles with absolute subcutaneous bioavailability of 31.1 plus or minus 6.2% (Gu et al., Drug Metabolism and Pharmacokinetics, 2016;31(1):51-56).

Research status

Discovery and an early dispute. The 1970 Nature report launched a long run of work on phagocyte stimulation, summarized in the Fridkin and Najjar review, and its central claim was contested almost immediately. Cooper et al., Inflammation, 1982;6(1):103-112, measured chemiluminescence during phagocytosis and uptake of radiolabeled bacteria using serum from splenectomized patients, presumed to lack tuftsin, against normal serum, with and without added tuftsin; no differences appeared in either assay, and the authors questioned whether tuftsin alters phagocytosis by human polymorphonuclear neutrophils. The tetrapeptide also proved non-antigenic, with attempts to raise anti-tuftsin antibodies failing (Naim et al., Immunological Investigations, 1989;18(6):817-824).

Tuftsin deficiency in humans. The most durable human finding is an association between impaired splenic function and low measured tuftsin activity. Tuftsin activity was lower in patients with AIDS, AIDS-related complex and splenectomy than in healthy volunteers, and correlated inversely with splenic function (Corazza et al., Lancet, 1991;337(8732):12-13). Impaired splenic function and tuftsin deficiency were likewise found in patients with intestinal failure on long-term intravenous nutrition (Zoli et al., Gut, 1998;43(6):759-762). In patients with cirrhosis, tuftsin activity was lower than in healthy subjects, deficient neutrophil phagocytic activity correlated with tuftsin activity and normalized when synthetic tuftsin was added in vitro, and low activity was associated with more bacterial infections without an effect on survival (Trevisani et al., Gut, 2002;50(5):707-712). The effect of liver transplantation on both measures was examined later (Foschi et al., International Archives of Allergy and Immunology, 2005;137(3):258-262).

Human administration. Documented human exposure to tuftsin itself is confined to a small oncology program in the 1980s, including a study of tuftsin with cyclophosphamide in non-small-cell carcinoma of the lung (Warner et al., Chemioterapia, 1987;6(2 Suppl):706-708). It was not followed by a registered development program.

Imaging the tuftsin receptor. The one modern human study of a tuftsin-directed agent was diagnostic. The technetium-99m labeled peptide chelate RP128, designed to target the tuftsin receptor on phagocytes, went through a human dosimetry study and first clinical imaging in patients with active rheumatoid arthritis, visualizing synovia and detecting inflamed joints (Caveliers et al., Journal of Nuclear Medicine, 2001;42(1):154-161). The agent was not developed further.

Demyelinating disease models. The largest preclinical program ran at Stony Brook University. Modulation of microglial and macrophage activation by the tuftsin fragment TKP or by tuftsin itself attenuated the course of experimental autoimmune encephalomyelitis (Bhasin et al., BMC Immunology, 2007;8:10). Tuftsin promoted an anti-inflammatory switch, downregulated Th1 responses while expanding Th2 responses and regulatory T cells, and attenuated symptoms in the same model (Wu et al., PLoS One, 2012;7(4):e34933). Benefit was receptor dependent, as ablating neuropilin-1 in microglia abolished the improvement (Nissen and Tsirka, Glia, 2016;64(6):923-936). Combining tuftsin with a remyelinating therapy improved outcomes in models of central nervous system demyelinating disease, with tuftsin supplying the anti-inflammatory shift (Thompson et al., Frontiers in Immunology, 2018;9:2784). All of this evidence is in rodents. The tuftsin fragment 1-3, Thr-Lys-Pro, was protective in an animal model of intracerebral hemorrhage when delivered after injury (Wang et al., Annals of Neurology, 2003;54(5):655-664).

Tuftsin-phosphorylcholine. A Tel Aviv group built a bifunctional molecule linking tuftsin to phosphorylcholine to reproduce the immunomodulation seen with helminth infection. In lupus-prone mice with established nephritis it ameliorated disease about as well as methylprednisolone (Shemer et al., Clinical and Experimental Immunology, 2018;193(2):160-166). It also improved established collagen-induced arthritis (Blank et al., PLoS One, 2018;13(8):e0200615). Comparable preclinical signals were reported in giant cell arteritis tissue models (Croci et al., Journal of Autoimmunity, 2019;98:113-121), murine chronic colitis (Ben-Ami Shor et al., Journal of Clinical Medicine, 2019;9(1):65) and experimental autoimmune encephalomyelitis (Novikova et al., Journal of Neuroimmunology, 2019;337:577070). No clinical trial of the conjugate is registered.

Carrier and conjugate work. The active contemporary use of the sequence is as a targeting element. Liposomes bearing tuftsin have carried antimicrobial and anticancer agents in models of tuberculosis, leishmaniasis, malaria and cryptococcosis (Khan, Current Drug Targets, 2021;22(7):770-778), and a tuftsin-tailored lidamycin fusion protein inhibited growth of circulating gastric tumor cells associated with macrophage phagocytosis (Yuan et al., Biochemistry and Biophysics Reports, 2023;34:101443). Most recently, bifunctional phagocytic synapse enhancers pairing a PD-L1 binder with tuftsin were reported to bridge tumor PD-L1 to macrophage neuropilin-1 and remodel the tumor microenvironment (Sabatino et al., Cancer Research, 2026).

Registry and regulatory position. As of November 2026 ClinicalTrials.gov returns no study records for tuftsin, Drugs@FDA lists no application, and DailyMed holds no labeling. Related tetrapeptides have the same standing: Rigin was isolated from human IgG as another phagocytosis-stimulating tetrapeptide (Veretennikova et al., International Journal of Peptide and Protein Research, 1981;17(4):430-435) and is also unapproved. The extended analogs Selank and N-Acetyl-Selank carry a separate Russian evidence base, including reports that selank alters expression of inflammation-related genes in mice (Kolomin et al., Molecular Immunology, 2014;58(1):50-55).

Common dosage forms

• No approved presentation. No tuftsin product is marketed in any jurisdiction, so no vial, ampoule, tablet or pen strength exists.
• Investigational parenteral solutions. The 1980s oncology studies used synthetic tuftsin in solution for injection, prepared per protocol rather than supplied as a finished presentation.
• Research-grade peptide. The free tetrapeptide and the diacetate salt are listed as lyophilized powders for laboratory use.
• Conjugate and carrier formats. In current work the sequence is presented on the lipid bilayer of liposomes after palmitoylation, as a fused tail on recombinant proteins, or as one arm of a bifunctional engager, none of which is a finished dosage form.

Key considerations

• Regulatory status. The Research Market status reflects the absence of any approved tuftsin product. Drugs@FDA lists no application and DailyMed holds no labeling. ClinicalTrials.gov lists no registered study of the peptide as of November 2026, and no tuftsin product is approved outside the US either.
• The receptor was identified decades after the peptide. Neuropilin-1 was only shown to be the binding site in 2006, and the signaling route only in 2013. Claims drawn from the extensive earlier literature rest on an unidentified receptor and on assays that modern work has not always reproduced.
• Human evidence is thin, old and mostly observational. The deficiency studies measure an activity assay in patients with impaired splenic function and establish an association with infection risk, not that giving tuftsin prevents infection. The only interventional human data are a small oncology report from the 1980s and one phase 1 imaging study of a labeled analog.
• Efficacy claims come from rodent models. The strongest positive results, in experimental autoimmune encephalomyelitis, demyelination, lupus nephritis and collagen-induced arthritis, are rodent findings. Rapid peptidase degradation of the free tetrapeptide remains the obstacle that stabilized derivatives were designed to address.
• Naming and related molecules. Tuftsin, taftsin, TKPR and tuftsin diacetate all denote the same tetrapeptide. The fragment Thr-Lys-Pro and tuftsin-phosphorylcholine, T peptide, TKPPR, RP128, rigin and the selank heptapeptides are separate compounds that contain or derive from the sequence rather than aliases for it.