A New Kind of Immune Therapy Comes to San Diego:

Bottom Line Up Front

JANX014 is an experimental prostate-cancer immunotherapy now in its earliest stage of human testing (Phase 1) for men with metastatic castration-resistant prostate cancer (mCRPC). It is a "double-masked" T-cell engager — a drug engineered to stay switched off in the bloodstream and turn on only after it reaches the tumor, an approach meant to widen the safety margin and reduce the immune-overactivation reaction (cytokine release syndrome) that has limited earlier drugs of this type.

It is made by San Diego–based Janux Therapeutics, and the study is recruiting at six U.S. centers — the first of which is UC San Diego's Moores Cancer Center, right here at home. The study opened in April 2026 and aims to enroll about 43 men.

Important perspective: This is a first-in-human safety study. There are no efficacy results for JANX014 yet. Interest in it rests on the strong early results of its "cousin" drug JANX007 and of a competing double-masked drug, VIR-5500 — not on JANX014's own data, which does not exist so far.

The Trial at a Glance

Drug: JANX014 (a PSMA-directed, double-masked T-cell engager)
Maker: Janux Therapeutics, San Diego, CA (Nasdaq: JANX)
Who: Adults with metastatic castration-resistant prostate cancer (mCRPC)
Phase: Phase 1, first-in-human, open-label, multicenter
Design: Two parts — a dose-escalation stage that raises the dose cohort by cohort to find the maximum tolerated dose, then a dose-expansion stage at a dose already found tolerable. Given by IV (intravenous) infusion.
Enrollment: About 43 participants
Locations: 6 U.S. sites, including UC San Diego Moores Cancer Center
Timeline: Started April 15, 2026; estimated completion March 2029
Registry ID: NCT07545811 (protocol PRCA-014-001)
Status: Recruiting (registry last updated September 3, 2026)
Study contact: Janux Therapeutics · +1 858-206-8471 · PRCA-014-001_ct.gov@januxrx.com

What is a "T-cell engager," in plain terms?

Our immune system's T cells are natural cancer killers, but prostate tumors are good at hiding from them. A T-cell engager (TCE) is a lab-made antibody with two "hands." One hand grabs a protein found on prostate cancer cells; the other hand grabs a T cell. By physically pulling the two together, the drug forces the T cell to recognize and destroy the cancer cell.⁵

The protein JANX014 grabs onto is PSMA (prostate-specific membrane antigen) — the same marker used in PSMA-PET scans and targeted by the radioactive drug Pluvicto (¹⁷⁷Lu-PSMA-617). PSMA sits in large amounts on most prostate cancer cells, which makes it an attractive "address" for delivering treatment.³

The catch with T-cell engagers has been safety. When you switch T cells on, they release a flood of immune signaling chemicals. If that happens too broadly, patients can develop cytokine release syndrome (CRS) — fevers, chills, drops in blood pressure, and in severe cases something requiring hospital care. Older T-cell engagers also risked attacking healthy tissues that carry a little of the target protein. Overcoming these problems is the central engineering challenge in this field.¹³

Quick glossary

mCRPC — metastatic castration-resistant prostate cancer; disease that has spread and is growing despite hormone therapy.

PSMA — a protein on prostate cancer cells used both for imaging and as a treatment target.

PSA50 / PSA90 — a drop in the PSA blood marker of at least 50% or 90%; a common early sign a treatment is working.

CRS — cytokine release syndrome; a treatable but sometimes serious immune over-reaction, graded 1 (mild) to 5.

rPFS — radiographic progression-free survival; how long before scans show the cancer growing again.

What "double-masked" means — and why it matters

This is the feature that makes JANX014 newsworthy. Janux builds its drugs on a platform it calls TRACTr (Tumor-Activated T-Cell Engager). The idea is to attach removable "masks" over the drug's active parts so the medicine travels through the bloodstream in an inert, folded-up state. Tumors tend to be rich in certain cutting enzymes (proteases); when the drug reaches the tumor, those enzymes snip the masks off and the drug wakes up right where it is needed. The goal is to spare healthy tissue and blunt the CRS reaction.²

Janux's lead drug, JANX007, is single-masked. JANX014 goes a step further and masks both business ends — the PSMA-grabbing hand and the T-cell-grabbing (CD3) hand. In theory, two locks are harder to open in the wrong place than one, which could widen the safety margin further and allow more convenient dosing.¹ Janux has described JANX014 as an exploratory extension of its prostate program, growing out of research it began in early 2024 into several different PSMA-directed designs.⁴

The local angle

Janux Therapeutics is headquartered on Vista Sorrento Parkway in San Diego, so this research is very much a hometown story — and the trial is recruiting right here. The government registry lists six U.S. sites, with UC San Diego Moores Cancer Center at the top of the list:⁵

UC San Diego Moores Cancer Center — San Diego, CA
Washington University School of Medicine — St. Louis, MO
Medical University of South Carolina, Hollings Cancer Center — Charleston, SC
Prisma Health Cancer Institute — SC
SCRI Oncology Partners — Nashville, TN
SCRI at Mary Crowley — Dallas, TX

The study's general contact line is +1 858-206-8471 (or PRCA-014-001_ct.gov@januxrx.com). Because sites and openings can change, the surest step is to check the live record at clinicaltrials.gov/study/NCT07545811 and, most importantly, talk with your own oncologist.

Who the study is looking for

Eligibility is specific, and a few points stand out for our community. The trial is for men 18 or older with confirmed prostate adenocarcinoma that has become castration-resistant and spread. In the dose-escalation stage, it is aimed at men whose cancer has progressed after at least one novel antiandrogen (such as abiraterone, enzalutamide, apalutamide, or darolutamide) and at least one taxane chemotherapy regimen — though men who have declined taxane or can't safely take it may still qualify. The later dose-expansion stage looks for men who have had less prior treatment.⁵

Just as important is who is excluded. The trial does not accept men who have already had radioligand therapy (such as Pluvicto), any prior T-cell engager, or CAR-T cell therapy, or who have a prior solid-organ transplant or clinically significant heart disease.⁵ The Pluvicto exclusion is the one most likely to matter for our members: if you have already been treated with ¹⁷⁷Lu-PSMA-617, this particular trial would not be an option — a concrete reason the "is this for me?" question has to be worked out with your care team, not in the abstract.

Why the excitement, when JANX014 has no results yet?

Two things feed the optimism: the track record of Janux's related drug, and a strikingly similar competitor.

1. Janux's lead drug, JANX007

JANX007 (the single-masked PSMA T-cell engager) has produced some of the most encouraging early prostate-cancer immunotherapy data seen to date. In heavily pre-treated men — a group with few options left — early cohorts showed deep drops in PSA, and the safety profile was manageable, with CRS generally limited to the first treatment cycle and to milder grades.¹⁰ In its December 2025 update, Janux reported that, as of an October 2025 data cutoff, 109 patients had been treated across the Phase 1 program, with durable responses and radiographic progression-free survival in the range of roughly 7.9 to 8.9 months — and no Grade 3 CRS at clinically relevant doses.⁸ JANX007 has moved into expansion cohorts in taxane-naïve patients, including a combination with the hormonal agent darolutamide (Nubeqa). The company expects to present additional JANX007 data at a medical meeting in the first half of 2027.⁷

2. A near-twin competitor: VIR-5500

The concept behind JANX014 is not Janux's alone. Vir Biotechnology is developing VIR-5500, which is also a double-masked, PSMA-targeting T-cell engager (using a different masking technology called PRO-XTEN). At the ASCO Genitourinary Cancers Symposium in February 2026, Vir reported that in its highest-dose cohorts, 82% of evaluable patients had a PSA50 decline and 53% had a PSA90 decline, with a 45% objective (imaging) response rate, no dose-limiting toxicities, and only low-grade CRS. Notably, investigators reported no hearing loss — a specific "off-target" side effect that has troubled some other prostate T-cell engagers — which they attributed to the benefit of dual masking.¹⁴¹⁵ The program drew a major partnership: in February 2026, Astellas agreed to a deal worth up to about $1.7 billion (with $335 million upfront) to co-develop it.¹⁶

In other words, an independent company using the same "double-masked PSMA" strategy has now shown real patient responses. That is the strongest external reason to watch JANX014 closely — while remembering that JANX014 must still prove itself on its own.

Where JANX014 sits in the wider field

Prostate-cancer T-cell engagers are one of the most active areas in the disease right now. The table below places JANX014 among the drugs most often discussed alongside it. Note that the response numbers belong to the other drugs; JANX014's own column is deliberately blank because its trial has only just begun.

A snapshot of PSMA/STEAP1 T-cell engagers in prostate cancer (data as reported at 2024–2026 meetings and company releases; not head-to-head comparisons).
Drug (maker)	Target & design	Stage	Reported early activity
JANX014 (Janux)	PSMA, double-masked TCE	Phase 1, just started (2026)	No results yet
JANX007 (Janux)	PSMA, single-masked TCE	Phase 1/1b, expanding	Deep PSA responses; rPFS ~7.9–8.9 mo; no Grade 3 CRS at active doses⁸
VIR-5500 (Vir / Astellas)	PSMA, double-masked TCE	Phase 1; Phase 3 planned 2027	82% PSA50, 53% PSA90, 45% ORR at top doses¹⁴
Xaluritamig / AMG 509 (Amgen)	STEAP1 (not PSMA), unmasked TCE	Two Phase 3 trials (most advanced in class)	Potent activity in first-in-human study; CRS ~72%, mostly cycle 1¹¹¹³

Amgen's xaluritamig is worth knowing about because it is the furthest along of any prostate T-cell engager, already in two large Phase 3 studies (XALute and XALience).¹¹¹² It aims at a different target (STEAP1 rather than PSMA) and is not masked, and its early studies showed higher rates of CRS — which is precisely the problem the masked drugs are trying to solve.

The company behind the trial

For members who like to understand the business footing of a program — because a well-funded sponsor is more likely to see a trial through — Janux reported roughly $971 million in cash and investments as of June 30, 2026, which it says supports its clinical programs.⁷ In early 2026 the company earned a $35 million milestone payment under a collaboration with Bristol Myers Squibb.⁶ During the same period Janux discontinued a separate, non-prostate drug (JANX008, aimed at EGFR) after its early phase, and re-focused resources — a normal part of drug development, but a reminder that not every candidate advances.⁶ A third prostate drug, JANX013 (designed to be given with JANX007), was slated to enter the clinic in the second half of 2026.⁷

On the legal front: a review of public records and regulatory filings turned up no material lawsuits or shareholder litigation specific to the JANX014 program or its disclosures as of this writing. (The standard "forward-looking statement" language in Janux's press releases refers to a 1995 securities law by routine convention, not to any active case.)

What this means for patients and caregivers

It is genuinely encouraging that immune-based treatments — long a tough nut to crack in prostate cancer — are finally showing meaningful, repeatable responses in men who have run out of standard options. The "masking" strategy is a thoughtful answer to the safety problems that held earlier drugs back, and having two independent companies (Janux and Vir) validate the double-masked PSMA approach is a real positive sign for the field.

At the same time, honesty requires keeping expectations calibrated:

• JANX014 is at the very beginning. Phase 1 exists mainly to find a safe dose; benefit is not the primary question yet, and there are no JANX014 results to report.
• Early PSA responses, however deep, are not the same as living longer or better. Those answers require larger, longer studies.
• Eligibility for these trials is specific, and enrollment slots and locations shift over time.

How to Weigh a Phase 1 Trial

A patient's-eye guide to the question, "Is an early trial like this right for me?"

Start with what Phase 1 is actually asking. In this study, the main goals are safety questions — the rate of dose-limiting toxicities and side effects, and how the drug behaves in the body. PSA response, overall response rate, and rPFS are listed as secondary goals.⁵ In plain language: a Phase 1 trial is designed to answer "is it safe, and at what dose," not "will it shrink my cancer." Benefit is hoped for, never promised.

The honest trade-offs.

Against: This is the first time this exact drug has been given to humans, so there is no track record for it specifically. Early dose cohorts get low doses chosen for caution — possibly too low to help. T-cell engagers can cause cytokine release syndrome and other side effects that require close monitoring. And trials mean extra visits, IV infusions, and travel.
In favor: The escalation stage is aimed at men whose standard options are thinning, which changes the math. The underlying approach is less of a leap than a typical first-in-human drug: a closely related Janux drug (JANX007) and an independent double-masked competitor (VIR-5500) have both already shown real responses with mostly mild CRS. Trials also come with attentive, structured medical oversight.

The question that matters most is always: compared to what? A trial's appeal depends heavily on what proven options remain for you, how you personally weigh uncertainty against quality of life, and whether the logistics fit your life. There is no universal right answer.

Questions worth bringing to your oncologist

Given my history, do I even meet the eligibility criteria — and does anything (like prior Pluvicto) rule me out?
Which dose cohort is enrolling right now, and is it a low starting dose or a higher one?
What proven, standard options do I still have if I don't enroll — and what might I give up by choosing the trial?
What is the monitoring and visit schedule, and what happens during the cytokine-release watch window?
What are the most likely and most serious side effects, and how are they managed here?
Can I leave the trial if I change my mind, and what care would I get afterward?
Who is the principal investigator at the site, and can I speak with the trial coordinator directly?

A clinical-trials navigator or a second opinion at a comprehensive cancer center can also help you think it through without pressure.

If any of this feels relevant to your own situation, the right next step is a conversation with your treating oncologist or a clinical-trials navigator, who can weigh it against where you are in your own journey. As always, the IPCSG will keep tracking these programs and report new data as it emerges — the next meaningful readouts for the related JANX007 program are expected in 2027.

This article is provided for education and general information for the prostate-cancer community. It is not medical advice and is not a recommendation for or against any treatment or trial. Clinical trials involve risk, and eligibility and results vary. Please discuss any treatment decision with your own physician. Information is current as of September 2026 and drawn from the sources listed below; details may have changed since publication.

Sources

Janux Therapeutics. "Janux Therapeutics Announces First Participant Dosed in Phase 1 Study of JANX014." News release, April 16, 2026. investors.januxrx.com
Janux Therapeutics. "PSMA-TRACTr (JANX014)" program page and TRACTr platform description. januxrx.com/psma-tractr-janx014
Clarke H. "PSMA-targeted T-cell engager enters phase 1 testing in mCRPC." Urology Times, April 20, 2026. urologytimes.com
"First Patient Dosed in JANX014 Trial in Metastatic CRPC." Targeted Oncology, 2026. targetedonc.com
U.S. National Library of Medicine. "Study of JANX014 in Subjects With Metastatic Castration-Resistant Prostate Cancer" (protocol PRCA-014-001), ClinicalTrials.gov Identifier NCT07545811. Sponsor: Janux Therapeutics. Status: Recruiting; record last updated September 3, 2026 (source of study design, six locations, enrollment target, eligibility, and endpoints cited here). clinicaltrials.gov/study/NCT07545811
Janux Therapeutics. "Janux Therapeutics Reports First Quarter 2026 Financial Results and Business Highlights." May 7, 2026 (JANX014 initiation; JANX008 discontinuation; Bristol Myers Squibb milestone). businesswire.com
Janux Therapeutics. "Janux Therapeutics Reports Second Quarter 2026 Financial Results and Business Highlights." August 6, 2026 (enrollment status; cash position; upcoming milestones). investors.januxrx.com
Janux Therapeutics. "Janux Announces Encouraging Efficacy and Safety Profile from Ongoing Phase 1 Clinical Trial for JANX007 in mCRPC." December 2025 (rPFS 7.9–8.9 months; 109 patients as of Oct 15, 2025 cutoff). investors.januxrx.com
Janux Therapeutics. "Janux Announces Doses Selected for Phase 1b Expansion Trials… for JANX007 in mCRPC." December 2, 2024 (100% PSA50, 63% PSA90, 31% PSA99 in first 16 patients). businesswire.com
"JANX007 demonstrates encouraging clinical activity in mCRPC." Urology Times. urologytimes.com
Amgen Inc. Form 8-K earnings release, quarter ended June 30, 2026 (xaluritamig XALute and XALience Phase 3 status). U.S. Securities and Exchange Commission. sec.gov
"ASCO 2026: XALience — A Phase 3 Study of Xaluritamig + Abiraterone Versus Investigator's Choice in Chemotherapy-Naïve mCRPC." UroToday, June 2026. urotoday.com
Kelly WK, et al. "Xaluritamig, a STEAP1 × CD3 XmAb 2+1 Immune Therapy for Metastatic Castration-Resistant Prostate Cancer: Results from Dose Exploration in a First-in-Human Study." Cancer Discovery (PubMed). pubmed.ncbi.nlm.nih.gov/37861461
Vir Biotechnology. "Vir Biotechnology Reports Positive Updated Phase 1 Results for PSMA-targeting, PRO-XTEN Dual-masked T-Cell Engager VIR-5500 in Patients with Metastatic Prostate Cancer." February 23, 2026. investors.vir.bio
De Bono J, et al. "Preliminary phase 1 dose escalation results of VIR-5500 (AMX-500), a dual-masked PRO-XTEN T-cell engager, in mCRPC." ASCO GU 2026, Abstract 17; conference coverage via UroToday. urotoday.com
Kansteiner F. "Astellas says 'I do' to Vir's T-cell engager in $1.7B deal." Fierce Biotech, February 25, 2026. fiercebiotech.com
Janux Therapeutics. "Janux Therapeutics Reports Fourth Quarter and Full Year 2025 Financial Results and Business Highlights." February 26, 2026 (Bristol Myers Squibb collaboration; JANX007 program summary). investors.januxrx.com

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