transform.interceptor.ts

import {
  NestInterceptor,
  ExecutionContext,
  Injectable,
  CallHandler,
} from '@nestjs/common';
import { classToPlain } from 'class-transformer';
import { map } from 'rxjs/operators';

@Injectable()
export class TransformInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler<any>) {
    return next.handle().pipe(map(data => classToPlain(data)));
  }
}

as @royeradames and @ysuzuki19 suggests, instanceToPlain is the way to take off the deprecated. See the doc:

typestack/class-transformer@v0.5.0...v0.5.1#diff-a2a171449d862fe29692ce031981047d7ab755ae7f84c707aef80701b3ea0c80R15

Assuming v0.5.1