Add TULIP-TCR pMHC:TCR binding predictor

[iskandr]

Adds a Tulip predictor wrapping TULIP-TCR — pMHC:TCR binding, like NetTCR, but it also takes the presenting MHC allele as an input.

Stacked on #221. Base is support-unnormalizable-alleles; GitHub will retarget to master once #221 merges. Review #221 first. Version 3.19.0 → 3.20.0.

The licensing/isolation problem (why this looks different from other predictors)

TULIP-TCR is GPLv3 and is coupled to transformers==4.32.1 (its model code is a fork of that release's internals). mhctools is Apache-2.0 and depends on neither torch nor transformers. So this wrapper vendors none of TULIP — no source, no weights, no tokenizers. It runs a user-provided checkout out-of-process, in a separate interpreter, by invoking TULIP's own predict.py via subprocess — the same "shell out to a user-provided install" pattern already used for the DTU netMHC* tools and NetTCR. Nothing in mhctools imports TULIP's GPL code, so the Apache package stays clean.

This is a deliberate deviation from "bundle the weights": bundling GPL weights/source into an Apache package isn't license-clean, and the external-checkout pattern is both correct and consistent with the existing predictors.

Setup (two env vars)

• TULIP_HOME — a clone of TULIP-TCR (predict.py, src/, tokenizers, released model_weights/).
• TULIP_PYTHON — an isolated Python 3.11 interpreter with torch + transformers==4.32.1.

scripts/setup_tulip_env.sh does both (clones TULIP, builds the env via uv or venv+pip, smoke-tests the import).

Why 3.11 specifically: transformers==4.32.1 resolves tokenizers 0.13.x, which has no cp312 wheel — on 3.12 it builds from source and needs a Rust toolchain. On 3.11 a prebuilt wheel exists, so the install is wheels-only. (Confirmed empirically: modern transformers does not work — TULIP breaks at model construction on BertConfig.cross_attention_hidden_size, removed in 5.x — so the old pin is required, not optional.)

Usage

from mhctools import Tulip, TCR

tcr = TCR(cdr3a="CAGASGNTGKLIF", cdr3b="CASSIRASYEQYF", name="clone1")
predictor = Tulip()                       # reads TULIP_HOME + TULIP_PYTHON
results = predictor.predict(["GILGFVFTL"], [tcr], mhc="HLA-A*02:01")
results[0].preds[0].score                 # TULIP log-likelihood; higher = more likely binding

predict(peptides, tcrs, mhc=...), predict_pairs([(peptide, TCR[, mhc]), ...]), and predict_dataframe(...) mirror NetTCR. Kind is pMHC_TCR_binding with mhc_dependence="single_allele".

How the bridge works

The wrapper writes an input CSV, runs predict.py in the checkout (cwd=TULIP_HOME so aatok/, mhctok/, src/ resolve), and maps the per-peptide output scores back to each (peptide, MHC, CDR3a, CDR3b) by position — predict.py doesn't echo the MHC column, so content-joining wouldn't disambiguate same-peptide/different-MHC rows; position within each peptide group does.

Tests & CI

• tests/test_tulip.py: binary-free unit tests mock the subprocess to cover input-CSV construction, per-peptide output parsing, position/score mapping, MHC pass-through, dedup, and error propagation (added to the public CI subset, runs on all Python versions). End-to-end tests run only when TULIP_HOME + TULIP_PYTHON are set.
• New integration-tulip CI job: builds the isolated Python-3.11 sidecar, clones the public TULIP repo, and runs the wrapper end-to-end.

Local full suite: 526 passed, 38 skipped, 2 xfailed (real netMHCpan 4.2 + a real TULIP sidecar; end-to-end scores match predict.py's own output exactly).

https://claude.ai/code/session_01LZahFhBSCiehXTESCYQ7wG

[iskandr]

Auto-closed when the stacked base branch support-unnormalizable-alleles was deleted on the #221 merge. Reopened as #232 (same commit, rebased onto master).