# Thymosin Alpha-1 & LL-37: What the Research Says About Immune-Modulating Peptides

Evidence & Research Status

Evidence LevelPreclinical / Early-Stage Research

FDA StatusNot FDA-approved for human use

Regulatory StatusResearch Use Only (RUO) — not for human consumption

Last UpdatedAugust 5, 2026

What This Article Covers

The immune system is usually split into two branches: innate immunity, the fast, non-specific first response, and adaptive immunity, the slower, highly specific response that builds memory over time…

Primary References [pubmed.ncbi.nlm.nih.gov](https://pubmed.ncbi.nlm.nih.gov/40969554/) [pmc.ncbi.nlm.nih.gov](https://pmc.ncbi.nlm.nih.gov/articles/PMC5025565/)

Evidence Level reflects the general state of published research for this compound category and is not a claim about the safety, efficacy, or approval status of any product sold on this site. All compounds are offered strictly for research use.

*By Charles Fowler, Founder of Portal to Wellness · Last reviewed: July 2026 · ~9 min read*

*A quick note on why I wrote this: I’m not a doctor or an immunologist — I’m a founder who spends my days reading the peptide literature and vetting what we carry. Thymosin Alpha-1 and LL-37 both get called “immune peptides,” but they work on almost opposite ends of the immune system, and the research behind each is a genuinely interesting contrast — one of the most clinically documented peptides in immunology on one side, and a newer, more mechanistic body of antimicrobial research on the other. Everything below is educational only, reflects published, publicly available research, and is not medical advice.*

Key Takeaways

- Thymosin Alpha-1 and LL-37 target opposite ends of the immune system — adaptive vs. innate immunity.
- Thymosin Alpha-1 has the deepest clinical trial record of the two, especially in sepsis and vaccine-adjuvant research.
- LL-37’s evidence base is largely preclinical and mechanistic, with one completed human wound-healing trial.
- Neither is FDA-approved in the U.S.; both are sold strictly for laboratory research use only.

## Two peptides, two halves of the immune system

The immune system is usually split into two branches: innate immunity, the fast, non-specific first response, and adaptive immunity, the slower, highly specific response that builds memory over time. Thymosin Alpha-1 and LL-37 sit on opposite sides of that split. Thymosin Alpha-1 primarily orchestrates the adaptive immune system, influencing T-cell maturation and dendritic cell function. LL-37 is a front-line innate immune peptide — part of the body’s built-in antimicrobial defense, produced directly by immune and epithelial cells at sites of infection or injury.

## Thymosin Alpha-1: one of the most clinically documented peptides in immunology

Thymosin Alpha-1 is a 28-amino-acid peptide originally isolated from thymus tissue. Unlike many research peptides, it has an unusually deep clinical trial record — it’s approved for clinical use in more than 35 countries (though notably not the United States, where it remains investigational) and has been studied in randomized controlled trials across several conditions:

- **Sepsis.** This is where the clinical evidence is strongest. A 2026 systematic review and meta-analysis pooling 11 randomized controlled trials and 1,927 septic patients found Thymosin Alpha-1 therapy was associated with a significantly lower mortality rate compared to standard care, alongside greater improvement in APACHE II severity scores. An earlier multicenter randomized trial (ETASS) reported similar directional findings specifically in severe sepsis.
- **Vaccine adjuvant use.** Research has examined Thymosin Alpha-1 as an adjuvant to influenza vaccination, with several studies reporting enhanced immune response to the vaccine in elderly and immunocompromised populations — groups that typically mount weaker vaccine responses on their own.
- **Oncology.** In cancer immunotherapy research, Thymosin Alpha-1 has been studied for its ability to activate dendritic cells and augment natural killer (NK) cell cytotoxicity against tumor cells, with investigational interest as an adjunct therapy in hepatocellular carcinoma, renal cell carcinoma, and non-small cell lung cancer.
- **Chronic viral infection.** Thymosin Alpha-1 has also been investigated in hepatitis B and hepatitis C trials, given its role in modulating T-cell-mediated antiviral response.

The mechanism proposed across this research is that Thymosin Alpha-1 helps regulate T-cell subsets and inflammatory mediators — essentially helping calibrate an immune response that’s either underperforming (as in vaccine non-responders or cancer) or dangerously overactive (as in sepsis), rather than simply “boosting” immunity in a blanket sense.

## LL-37: the body’s own antimicrobial peptide

LL-37 is the only cathelicidin-family antimicrobial peptide found in humans, cleaved from a precursor protein (hCAP18) and produced by neutrophils, epithelial cells, and other immune cells, particularly at wound sites and mucosal surfaces. Its research profile is built around direct, mechanistic antimicrobial and tissue-repair activity rather than large multicenter trials:

- **Broad-spectrum antimicrobial and anti-biofilm activity.** Research shows LL-37 has direct antimicrobial and anti-biofilm activity against a range of both Gram-positive and Gram-negative pathogens, which is part of why it’s been studied specifically for polymicrobial (multi-organism) infected wounds.
- **Wound healing.** Animal studies report that LL-37 significantly improves re-epithelialization and granulation tissue formation in experimental wounds, and it’s described in the literature as having a “pleiotropic” role — acting as an alarmin that helps orchestrate immune response to injury, locally modulating inflammation, and promoting angiogenesis alongside its antimicrobial function.
- **The one completed human interventional study.** A randomized controlled trial (Miranda et al., 2023, n=48) tested topical LL-37 cream against placebo in diabetic foot ulcers and found significantly increased granulation tissue formation in the LL-37 group. This remains the primary completed human interventional data point for LL-37 — the rest of the evidence base is preclinical and mechanistic.

## Complementary, not interchangeable

No clinical trials have combined Thymosin Alpha-1 and LL-37 in a single trial, so any combination use is based on mechanistic rationale rather than direct trial data. That rationale is straightforward, though: Thymosin Alpha-1’s research strength is systemic, adaptive-immune modulation, particularly relevant to chronic viral infection, sepsis, and oncology support. LL-37’s research strength is localized, innate-immune and antimicrobial activity, particularly relevant to wound and tissue-repair contexts. They’re studied as complementary tools targeting different layers of immune function, not as substitutes for one another.

## Frequently Asked Questions

**Is Thymosin Alpha-1 FDA-approved?**
No. Despite being approved for clinical use in more than 35 countries, Thymosin Alpha-1 remains investigational in the United States and is sold here strictly for laboratory research use only.

**What condition has the strongest clinical evidence for Thymosin Alpha-1?**
Sepsis has the most robust randomized controlled trial evidence, including a 2026 meta-analysis of 11 RCTs and nearly 2,000 patients showing a mortality benefit associated with Thymosin Alpha-1 therapy.

**Is LL-37 the same as an antibiotic?**
No. LL-37 is an endogenous antimicrobial peptide with a broader, multi-mechanism role that includes direct pathogen disruption, immune signaling, and tissue-repair promotion — a different mode of action than a traditional antibiotic, and it hasn’t been tested against antibiotics head-to-head in large human trials.

**Do Thymosin Alpha-1 and LL-37 work on the same part of the immune system?**
No. Thymosin Alpha-1 primarily influences adaptive immunity (T-cells, dendritic cells); LL-37 is part of the innate immune system’s first-line antimicrobial defense. That is why researchers describe them as complementary rather than redundant.

## References

- Efficacy of thymosin α1 for sepsis: a systematic review and meta-analysis of randomized controlled trials (2026). [pubmed.ncbi.nlm.nih.gov](https://pubmed.ncbi.nlm.nih.gov/40969554/)
- The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial. [pubmed.ncbi.nlm.nih.gov](https://pubmed.ncbi.nlm.nih.gov/23327199/)
- The efficacy of thymosin α1 as immunomodulatory treatment for sepsis: a systematic review of randomized controlled trials. [pmc.ncbi.nlm.nih.gov](https://pmc.ncbi.nlm.nih.gov/articles/PMC5025565/)
- The Human Cathelicidin Antimicrobial Peptide LL-37 as a Potential Treatment for Polymicrobial Infected Wounds. [pmc.ncbi.nlm.nih.gov](https://pmc.ncbi.nlm.nih.gov/articles/PMC3699762/)
- In vitro and in vivo wound healing-promoting activities of human cathelicidin LL-37. [pubmed.ncbi.nlm.nih.gov](https://pubmed.ncbi.nlm.nih.gov/17805349/)
- LL-37: Cathelicidin-related antimicrobial peptide with pleiotropic activity. [pubmed.ncbi.nlm.nih.gov](https://pubmed.ncbi.nlm.nih.gov/27117377/)
- The human cathelicidin LL-37 — a pore-forming antibacterial peptide and host-cell modulator. [pubmed.ncbi.nlm.nih.gov](https://pubmed.ncbi.nlm.nih.gov/26556394/)

📚 Part of our [Immune & Protective](https://portaltowellness.net/immune-modulators/) research guide.

*This article is for informational and educational purposes only. It is not medical advice and does not describe the diagnosis, treatment, cure, or prevention of any disease. Portal to Wellness does not sell products intended for human consumption or clinical use; all compounds referenced are sold strictly for laboratory research use only (RUO). Always consult a qualified healthcare professional before making any changes to your health routine.*

### Continue Your Research

Related Articles [DSIP & Epithalon: What the Research Says About Sleep and Circadian Peptides](https://portaltowellness.net/research/dsip-epithalon-what-the-research-says-about-sleep-and-circadian-peptides/) [Semax, Selank & Pinealon: What the Research Shows About Nootropic Peptides](https://portaltowellness.net/research/semax-selank-pinealon-what-the-research-shows-about-nootropic-peptides/)

Related Products [Thymosin Alpha-1 – 10mg/vial (Research Use Only)](https://portaltowellness.net/shop/thymosin-alpha-1/)

Related Research Guide [Research Compound Index](https://portaltowellness.net/research-compound-index/)

Related Category [Immune & Protective](https://portaltowellness.net/immune-modulators/)

Related FAQ [General Research & Ordering FAQ](https://portaltowellness.net/faq/)

More Research [Browse the full PTW Research Hub →](https://portaltowellness.net/research/)

## Amounts used in the published research

**These two compounds sit at opposite ends of the evidence spectrum** , and it is worth being clear about which is which. Thymosin alpha-1 is an approved medicine in roughly 30 countries with a regulator-reviewed label, formal pharmacokinetics and phase 3 trials in over a thousand patients. LL-37 has two topical wound trials totalling 182 patients, the larger of which was negative, and no systemic human dosing at all.

### Thymosin alpha-1 (thymalfasin / Zadaxin)

Thymosin alpha-1 (thymalfasin, marketed as Zadaxin) is approved in several countries for chronic hepatitis B; the label trials and later studies are summarised below.

| Setting | n | Outcome |
| --- | --- | --- |
| Chronic hepatitis B (label trials) | 223 | 36% vs 19% response at 12-month follow-up |
| Severe sepsis (ETASS) | 361 | 28-day mortality 26.0% vs 35.0%; primary endpoint marginal (p=0.062) |
| Sepsis (TESTS, phase 3) | 1,106 | **Negative** — 23.4% vs 24.1%, no benefit |
| Melanoma (Maio 2010) | 488 | No difference in response rate |

**Pharmacokinetics:** subcutaneous, Tmax 1–2 h, Cmax 30–80 µg/L, half-life about 2 hours, no accumulation over 5 days. Dose-proportional from 0.8 to 6.4 mg. Most common adverse effect is injection-site irritation.

**Status:** approved across Asia-Pacific, Latin America, Eastern Europe, the Middle East and Italy. **Not approved in the US, Japan, or most of Europe** — US orphan designations only, and in December 2024 an FDA advisory committee recommended *against* adding it to the compounding bulks list.

### LL-37 (human cathelicidin)

**No injectable, oral or systemic human study of LL-37 exists** , and no human pharmacokinetic or half-life data has been published. Both human trials were topical, applied to leg ulcers. The larger, later trial did not meet its endpoint.

| Trial | n | Outcome |
| --- | --- | --- |
| Phase I/II, venous leg ulcers | 34 | 0.5 mg/mL healed ~6× faster than placebo; **3.2 mg/mL was no better than placebo** |
| HEAL LL-37, phase IIb | 148 | **Negative** overall; benefit only in a post-hoc subgroup |

**The cytotoxicity figure matters more than the antimicrobial one.** LL-37 kills a range of bacteria at under 10 µg/mL, with a minimum inhibitory concentration around 5 µM against *E. coli* . But it is **cytotoxic to human cells at 13–25 µM** — only about 2.6–5× above the amount that kills bacteria. Published work documents red blood cell lysis and DNA fragmentation in human cells. That narrow window is the reason clinical development stalled at topical use.

Animal: 1 mg/kg IV in a neutropenic mouse sepsis model. Status: **no approvals anywhere** ; developed topically as ropocamptide, halted after phase IIb.

### Sources

Zadaxin approved label (BPOM) — [product label PDF](https://registrasiobat.pom.go.id/files/assesment-reports/01751602483.pdf)
FDA Pharmacy Compounding Advisory Committee review of Thymosin alpha-1, Dec 2024 — [FDA review](https://www.fda.gov/media/183892/download)
ETASS sepsis trial — [PMID 23327199](https://pubmed.ncbi.nlm.nih.gov/23327199/) ( [NCT00711620](https://clinicaltrials.gov/study/NCT00711620) )
TESTS phase 3, BMJ 2025 — [PMID 39814420](https://pubmed.ncbi.nlm.nih.gov/39814420/) ( [NCT02867267](https://clinicaltrials.gov/study/NCT02867267) )
Rost 1999, subcutaneous pharmacokinetics — [PMID 10027483](https://pubmed.ncbi.nlm.nih.gov/10027483/)
Grönberg 2014, LL-37 phase I/II — [PMID 25041740](https://pubmed.ncbi.nlm.nih.gov/25041740/) ·
Mahlapuu 2021, HEAL LL-37 phase IIb — [PMID 34687253](https://pubmed.ncbi.nlm.nih.gov/34687253/)
Johansson 1998, cytotoxicity threshold — [PMID 9452503](https://pubmed.ncbi.nlm.nih.gov/9452503/) ·
Ciornei 2005 — [PMID 15980359](https://pubmed.ncbi.nlm.nih.gov/15980359/)

Sold for research and identification purposes only. Not for human dosing, injection, or ingestion, and not for veterinary use. This page describes published research; it is not instructions for use. For guidance about your own situation, speak with a qualified healthcare professional.

---

Source: https://portaltowellness.net/research/thymosin-alpha-1-ll-37-what-the-research-says-about-immune-modulating-peptides/
Research use only. Terms: https://portaltowellness.net/research-use-only/