mrvi

name	mrvi
description	MrVI — multi-resolution variational inference for multi-sample scRNA-seq. Two-level hierarchical model that learns both a sample-unaware cell-state latent (u) and a sample-aware latent (z). Outputs per-cell sample-distance matrices for stratification discovery, plus differential-abundance / differential-expression between sample groups at single-cell resolution. Built on scvi-tools; GPU recommended.
license	BSD-3-Clause
metadata	null

MrVI: Multi-Resolution Variational Inference

Overview

MrVI tackles a recurring problem in multi-sample / multi-donor scRNA-seq: the same cell type can behave differently between samples, and you want to discover those differences without committing up front to one cluster resolution.

The model is a two-level hierarchical VAE:

Level	Latent	What it represents
1	u_n	Cell state, batch-corrected and sample-unaware — like a clean scVI embedding
2	z_n	Cell state with sample effects added back in — same cell type in different samples lives at slightly different points in z

That layered design lets you do two things you can't do with vanilla scVI:

1. Per-cell sample-distance matrices — for each cell, "how does this exact cell look across all samples?" Reveals stratification structure invisible at the cluster level.
2. Differential abundance / DE at single-cell resolution — compare sample groups without forcing a clustering first.

Decoder: multi-head attention over batch + sample covariates. Likelihood: negative binomial on raw counts.

When to Use This Skill

• Multi-donor / multi-condition scRNA-seq where you want to find patient-level subgroups based on molecular profiles, not pre-defined clinical metadata.
• Differential expression / abundance comparisons across sample groups where you don't want to commit to a leiden resolution first.
• Exploratory analysis on cohort studies (≥ 10 samples) — MrVI shines when you have many samples.
• When scVI batch correction is too aggressive — MrVI preserves sample-level variation in z while still giving you a clean u for clustering.

Not for:

• Single-sample analyses — MrVI's whole point is sample-level variation. Use scVI.
• Spatial data with low sample count — see resolvi instead.
• ATAC-seq or other modalities — MrVI is RNA-specific (NB likelihood).
• CPU-only — like all scvi-tools models, training is much faster on GPU.

Prerequisites

• Python 3.9+
• An scRNA-seq AnnData with raw counts in .X
• A sample column (sample_id, donor, patient, etc.) — the core covariate MrVI tracks
• Optional: batch column (different from sample — batch = technical, sample = biological)
• Optional: cell-type labels (improves analysis but not required)
• GPU strongly recommended

pip install scvi-tools

Quick Start

import scanpy as sc
import scvi
from scvi.external import MRVI
import torch

# ── 1. Load + sanity-check ──────────────────────────────────────────────
adata = sc.read_h5ad("cohort_data.h5ad")
# Required: raw counts in adata.X, sample column in adata.obs
assert "sample_id" in adata.obs.columns

# Standard pre-filter (MrVI does NOT do QC itself)
sc.pp.filter_cells(adata, min_genes=200)
sc.pp.filter_genes(adata, min_cells=3)

# Optionally select HVGs — MrVI scales linearly in n_genes, so trimming helps
sc.pp.highly_variable_genes(
    adata, n_top_genes=4000, flavor="seurat_v3",
    batch_key="sample_id"
)
adata = adata[:, adata.var["highly_variable"]].copy()

# ── 2. Setup ────────────────────────────────────────────────────────────
MRVI.setup_anndata(
    adata,
    sample_key  = "sample_id",         # CORE: per-sample target covariate
    batch_key   = "batch",             # OPTIONAL: nuisance batch column (different from sample)
    labels_key  = "cell_type",         # OPTIONAL: improves analysis if available
)

# ── 3. Build + train ────────────────────────────────────────────────────
model = MRVI(
    adata,
    n_hidden = 128,
    n_latent_u = 20,                   # cell-state latent dimensions
    n_latent_z = 20,                   # sample-aware latent dimensions
    n_layers   = 2,
)

model.train(
    max_epochs       = 400,
    accelerator      = "gpu",
    devices          = 1,
    early_stopping   = ,
)

model.save(, save_anndata=, overwrite=)

What MrVI Gives You

1. Two latent representations

# u: sample-unaware (clean cell-state, like batch-corrected scVI)
adata.obsm["U_mrvi"] = model.get_latent_representation(give_z=False)

# z: sample-aware (cell-state + sample effects)
adata.obsm["Z_mrvi"] = model.get_latent_representation(give_z=True)

Use U_mrvi for clustering and UMAP that you want clean of sample effects:

sc.pp.neighbors(adata, use_rep="U_mrvi")
sc.tl.umap(adata)
sc.tl.leiden(adata, resolution=0.5)
sc.pl.umap(adata, color=["leiden", "sample_id", "cell_type"])

Use Z_mrvi for analyses that should preserve sample effects (most of what's below).

2. Per-cell sample-distance matrices — the killer feature

For each cell, MrVI can compute "how different is this cell's profile across the N samples in the cohort?" This is a per-cell N × N matrix that you can mean-pool or cluster to find sample subgroups.

sample_dists = model.get_local_sample_representation(
    adata = adata,
    # batch_size = 32,   # lower if OOM
)
# Shape: (n_cells, n_samples, n_latent_z)
# Each cell has its own per-sample "where would I sit if I were sample X"

# Pairwise distance matrix per cell: (n_cells, n_samples, n_samples)
dist_mat = model.get_local_sample_distances(
    adata = adata,
    keep_cell = True,           # per-cell matrices (False → mean-pooled)
)

3. Cohort-level sample distances

Average those per-cell matrices to get a single N × N sample-distance matrix you can hierarchically cluster:

mean_dist = model.get_local_sample_distances(adata = adata, keep_cell = False)
# Shape: (n_samples, n_samples)

import scipy.cluster.hierarchy as sch
import matplotlib.pyplot as plt
import seaborn as sns

linkage = sch.linkage(mean_dist, method="average")
sns.clustermap(mean_dist, row_linkage=linkage, col_linkage=linkage,
                figsize=(8, 8), cmap="viridis")
plt.savefig("figures/sample_distance_clustermap.pdf")

The clustered heatmap reveals sample subgroups (e.g. responders vs non-responders) emerging from the molecular data alone, without any pre-defined grouping.

4. Per-cell differential abundance + differential expression

Compare two sample groups at single-cell resolution — no clustering required.

# Define your sample groups
adata.obs["group"] = adata.obs["sample_id"].map({
    "P01": "Disease", "P02": "Disease", ...,
    "P10": "Control", "P11": "Control", ...,
})

# Differential abundance — which cells become more/less common in disease?
da_df = model.differential_abundance(
    adata = adata,
    sample_cov_keys = ["group"],
    group1 = "Disease", group2 = "Control",
)
# Returns per-cell log-fold-change in abundance + significance

# Map onto the UMAP — where in the manifold does abundance change?
adata.obs["DA_log2FC"] = da_df["log2FC"].values
sc.pl.umap(adata, color=["DA_log2FC", "leiden"],
            vmin=-2, vmax=2, cmap="RdBu_r")

For DE (per-gene log-fold-change between sample groups, single-cell-resolution):

de_df = model.differential_expression(
    adata = adata,
    sample_cov_keys = ["group"],
    group1 = "Disease", group2 = "Control",
)
# Per-gene DE values aggregated per-cell — you can also stratify by cluster

Key Parameters

Model architecture

• n_latent_u (20): dimensions of the sample-unaware latent. Same intuition as scVI's n_latent.
• n_latent_z (20): dimensions of the sample-aware latent. Often kept equal to n_latent_u.
• n_hidden (128): neural-net width.
• n_layers (2): network depth.

Training

• max_epochs (400): MrVI typically needs more epochs than scVI to converge — the hierarchical model has more parameters.
• early_stopping (True): stops when validation loss stops dropping. Recommended.

Setup

• sample_key: required — the column MrVI builds its z representation around. Must be categorical.
• batch_key: technical batch (different from sample). E.g. "10X chemistry version" or "library prep date."
• labels_key: optional cell-type column. Improves downstream DE / DA analyses by stratifying.

Best Practices

• Raw counts in .X, not log-normalized. The NB likelihood needs counts.
• Use HVG selection before training to keep n_genes ≤ 5000. Training time is linear in n_genes.
• More samples = better. With < 5 samples, MrVI's sample-distance analysis is underpowered. Aim for ≥ 10, ideally 20-50.
• Sample ≠ Batch. Sample = biological unit (donor, patient). Batch = technical (run, chemistry). Pass them separately. If they're identical, just pass sample_key.
• For DA / DE, group sample IDs into sample-level covariates first. MrVI computes per-cell statistics by aggregating over sample-level grouping — your group1/group2 should be sample-level categories.
• Validate the U embedding first. Before trusting any per-cell sample-distance analysis, confirm UMAP-on-U gives a sensible cell-type structure. If U is noisy, everything downstream is unreliable.
• Cohort-mean distance vs per-cell distance — both useful. Mean for "which samples cluster together overall"; per-cell for "in which cell type does that grouping break down."

When MrVI Output Looks Wrong

Symptom	Likely cause	Fix
UMAP-on-U still shows sample-segregation	Under-trained or batch_key wasn't set	More epochs; verify the batch/sample distinction
Sample distances are uniform	Under-trained, or your samples really are similar	Inspect the loss curve; sometimes the biology is just homogeneous
differential_abundance returns NaN for many cells	Sample groups are too unbalanced	Re-balance, or remove samples in tiny groups
OOM during get_local_sample_distances	Per-cell N×N matrix is large	Use keep_cell=False for cohort-mean, or batch through cells manually

End-to-End Template

assets/mrvi_template.py — single parameterized script. Set sample / batch / group columns and the comparison groups, run end-to-end.

Convenience Scripts

• scripts/run_mrvi.py — CLI wrapper: train, save model, write augmented AnnData

References

• scvi-tools MrVI docs
• scvi-tools tutorials — multi-sample section
• Boyeau et al. (2024 preprint), Deep generative modeling for population-scale single-cell genomics (the MrVI paper; check the scvi-tools docs for the current citation)
• Related Operon protocols:
  • scanpy — upstream QC + HVG selection
  • hdwgcna — alternative cohort-level co-expression analysis (R-based)